Add position classes for new functions

This change adds a custom implementation of IScriptExtent similar to
InternalScriptExtent.  The major difference being the replacement of
PositionHelper with FileContext.  The PositionHelper class was used to
store the full script text and line start mapping for all ScriptExtent
objects of the same file.  FileContext is a great replacement for this
because it's already kept unique by PSES and it adapts to changes.

- Added FullScriptExtent and FullScriptPosition classes.

- Changed the scriptFile field on FileContext from private to internal.

Author: SeeminglyScience

src/PowerShellEditorServices/Extensions/FileContext.cs

@@ -16,7 +16,7 @@ public class FileContext
     {
         #region Private Fields
 
-        private ScriptFile scriptFile;
+        internal ScriptFile scriptFile;
         private EditorContext editorContext;
         private IEditorOperations editorOperations;
 

src/PowerShellEditorServices/Language/FullScriptExtent.cs

@@ -0,0 +1,168 @@
+using System.Management.Automation.Language;
+using Microsoft.PowerShell.EditorServices.Extensions;
+
+namespace Microsoft.PowerShell.EditorServices
+{
+    /// <summary>
+    /// Provides an IScriptExtent implementation that is aware of editor context
+    /// and can adjust to changes.
+    /// </summary>
+   public class FullScriptExtent : IScriptExtent
+    {
+        #region Properties
+
+        /// <summary>
+        /// Gets the buffer range of the extent.
+        /// </summary>
+        public BufferRange BufferRange { get; private set; }
+
+        /// <summary>
+        /// Gets the FileContext that this extent refers to.
+        /// </summary>
+        public FileContext FileContext { get; }
+
+        /// <summary>
+        /// Gets the file path of the script file in which this extent is contained.
+        /// </summary>
+        public string File
+        {
+            get { return FileContext.Path; }
+        }
+
+        /// <summary>
+        /// Gets the starting script position of the extent.
+        /// </summary>
+        public IScriptPosition StartScriptPosition
+        {
+            get { return new FullScriptPosition(FileContext, BufferRange.Start, StartOffset); }
+        }
+
+        /// <summary>
+        /// Gets the ending script position of the extent.
+        /// </summary>
+        public IScriptPosition EndScriptPosition
+        {
+            get { return new FullScriptPosition(FileContext, BufferRange.End, EndOffset); }
+        }
+
+        /// <summary>
+        /// Gets the starting line number of the extent.
+        /// </summary>
+        public int StartLineNumber
+        {
+            get { return BufferRange.Start.Line; }
+        }
+
+
+        /// <summary>
+        /// Gets the starting column number of the extent.
+        /// </summary>
+        public int StartColumnNumber
+        {
+            get { return BufferRange.Start.Column; }
+        }
+
+        /// <summary>
+        /// Gets the ending line number of the extent.
+        /// </summary>
+        public int EndLineNumber
+        {
+            get { return BufferRange.End.Line; }
+        }
+
+        /// <summary>
+        /// Gets the ending column number of the extent.
+        /// </summary>
+        public int EndColumnNumber
+        {
+            get { return BufferRange.End.Column; }
+        }
+
+        /// <summary>
+        /// Gets the text that is contained within the extent.
+        /// </summary>
+        public string Text
+        {
+            get
+            {
+                // StartOffset can be > the length for the EOF token.
+                if (StartOffset > FileContext.scriptFile.Contents.Length)
+                {
+                    return "";
+                }
+
+                return FileContext.GetText(BufferRange);
+            }
+        }
+
+        /// <summary>
+        /// Gets the starting file offset of the extent.
+        /// </summary>
+        public int StartOffset { get; private set; }
+
+        /// <summary>
+        /// Gets the ending file offset of the extent.
+        /// </summary>
+        public int EndOffset { get; private set; }
+
+        #endregion
+
+        #region Constructors
+
+        /// <summary>
+        /// Creates a new instance of the FullScriptExtent class.
+        /// </summary>
+        /// <param name="fileContext">The FileContext this extent refers to.</param>
+        /// <param name="bufferRange">The buffer range this extent is located at.</param>
+        public FullScriptExtent(FileContext fileContext, BufferRange bufferRange)
+        {
+            BufferRange = bufferRange;
+            FileContext = fileContext;
+
+            StartOffset = fileContext.scriptFile.GetOffsetAtPosition(
+                bufferRange.Start.Line,
+                bufferRange.Start.Column);
+
+            EndOffset = fileContext.scriptFile.GetOffsetAtPosition(
+                bufferRange.End.Line,
+                bufferRange.End.Column);
+        }
+
+        /// <summary>
+        /// Creates an new instance of the FullScriptExtent class.
+        /// </summary>
+        /// <param name="fileContext">The FileContext this extent refers to.</param>
+        /// <param name="startOffset">The zero based offset this extent starts at.</param>
+        /// <param name="endOffset">The zero based offset this extent ends at.</param>
+        public FullScriptExtent(FileContext fileContext, int startOffset, int endOffset)
+        {
+            FileContext = fileContext;
+            StartOffset = startOffset;
+            EndOffset = endOffset;
+            BufferRange = fileContext.scriptFile.GetRangeBetweenOffsets(startOffset, endOffset);
+        }
+
+        #endregion
+
+        #region Public Methods
+
+        public override string ToString()
+        {
+            return Text;
+        }
+
+        /// <summary>
+        /// Moves the start and end positions of the extent by an offset. Can
+        /// be used to move forwards or backwards.
+        /// </summary>
+        /// <param name="offset">The amount to move the extent.</param>
+        public void AddOffset(int offset) {
+            StartOffset += offset;
+            EndOffset += offset;
+
+            BufferRange = FileContext.scriptFile.GetRangeBetweenOffsets(StartOffset, EndOffset);
+        }
+
+        #endregion
+    }
+}

src/PowerShellEditorServices/Language/FullScriptPosition.cs

@@ -0,0 +1,57 @@
+using System.Management.Automation.Language;
+using Microsoft.PowerShell.EditorServices.Extensions;
+
+namespace Microsoft.PowerShell.EditorServices
+{
+    internal class FullScriptPosition : IScriptPosition
+    {
+        #region Fields
+        private readonly FileContext fileContext;
+
+        private readonly BufferPosition bufferPosition;
+
+        #endregion
+
+        #region Properties
+        public string File
+        {
+            get { return fileContext.Path; }
+        }
+        public int LineNumber
+        {
+            get { return bufferPosition.Line; }
+        }
+        public int ColumnNumber
+        {
+            get { return bufferPosition.Column; }
+        }
+        public string Line
+        {
+            get { return fileContext.scriptFile.GetLine(LineNumber); }
+        }
+        public int Offset { get; }
+
+        #endregion
+
+        #region Constructors
+
+        internal FullScriptPosition(FileContext context, BufferPosition position, int offset)
+        {
+            fileContext = context;
+            bufferPosition = position;
+            Offset = offset;
+        }
+
+        #endregion
+
+
+        #region Public Methods
+
+        public string GetFullScript()
+        {
+            return fileContext.GetText();
+        }
+
+        #endregion
+    }
+}