Revert "🔥Remove static Default getters, obsoleted by UnitsNetSetup" (#1480)

Reverts #1475

This reverts commit a3c32b6.

- Add back default getters
- Remove obsolete message, rewrite xmldoc a bit

Author: angularsen

UnitsNet/CustomCode/QuantityParser.cs

@@ -34,6 +34,14 @@ public class QuantityParser
         private readonly UnitAbbreviationsCache _unitAbbreviationsCache;
         private readonly UnitParser _unitParser;
 
+        /// <summary>
+        ///     The default singleton instance for parsing quantities.
+        /// </summary>
+        /// <remarks>
+        ///     Convenience shortcut for <see cref="UnitsNetSetup"/>.<see cref="UnitsNetSetup.Default"/>.<see cref="UnitsNetSetup.QuantityParser"/>.
+        /// </remarks>
+        public static QuantityParser Default => UnitsNetSetup.Default.QuantityParser;
+
         /// <summary>
         ///     Creates an instance of <see cref="QuantityParser"/>, optionally specifying an <see cref="UnitAbbreviationsCache"/>
         ///     with unit abbreviations to use when parsing.

UnitsNet/CustomCode/UnitAbbreviationsCache.cs

@@ -31,6 +31,15 @@ public sealed class UnitAbbreviationsCache
         /// </example>
         internal static readonly CultureInfo FallbackCulture = CultureInfo.InvariantCulture;
 
+        /// <summary>
+        ///     The default singleton instance with the default configured unit abbreviations, used for ToString() and parsing of quantities and units.
+        /// </summary>
+        /// <remarks>
+        ///     Convenience shortcut for <see cref="UnitsNetSetup"/>.<see cref="UnitsNetSetup.Default"/>.<see cref="UnitsNetSetup.UnitAbbreviations"/>.<br />
+        ///     You can add custom unit abbreviations at runtime, and this will affect all usages globally in the application.
+        /// </remarks>
+        public static UnitAbbreviationsCache Default => UnitsNetSetup.Default.UnitAbbreviations;
+
         private QuantityInfoLookup QuantityInfoLookup { get; }
 
         /// <summary>

UnitsNet/CustomCode/UnitParser.cs

@@ -13,13 +13,21 @@ namespace UnitsNet
 {
     /// <summary>
     ///     Parses units given a unit abbreviations cache.
-    ///     A static instance <see cref="UnitsNetSetup"/>.<see cref="UnitsNetSetup.Default"/>.<see cref="UnitsNetSetup.UnitParser"/> is used internally
-    ///     to parse quantities and units using the default abbreviations cache for all units and abbreviations defined in the library.
+    ///     The static instance <see cref="Default"/> is used internally to parse quantities and units using the
+    ///     default abbreviations cache for all units and abbreviations defined in the library.
     /// </summary>
     public sealed class UnitParser
     {
         private readonly UnitAbbreviationsCache _unitAbbreviationsCache;
 
+        /// <summary>
+        ///     The default singleton instance for parsing units from the default configured unit abbreviations.
+        /// </summary>
+        /// <remarks>
+        ///     Convenience shortcut for <see cref="UnitsNetSetup"/>.<see cref="UnitsNetSetup.Default"/>.<see cref="UnitsNetSetup.UnitParser"/>.
+        /// </remarks>
+        public static UnitParser Default => UnitsNetSetup.Default.UnitParser;
+
         /// <summary>
         ///     Create a parser using the given unit abbreviations cache.
         /// </summary>

UnitsNet/UnitConverter.cs

@@ -34,6 +34,15 @@ public delegate TQuantity ConversionFunction<TQuantity>(TQuantity inputValue)
     /// </summary>
     public sealed class UnitConverter
     {
+        /// <summary>
+        ///     The default singleton instance for converting values from one unit to another.<br />
+        ///     Modify this to add/remove conversion functions at runtime, such as adding your own third-party units and quantities to convert between.
+        /// </summary>
+        /// <remarks>
+        ///     Convenience shortcut for <see cref="UnitsNetSetup"/>.<see cref="UnitsNetSetup.Default"/>.<see cref="UnitsNetSetup.UnitConverter"/>.
+        /// </remarks>
+        public static UnitConverter Default => UnitsNetSetup.Default.UnitConverter;
+
         /// <summary>
         /// Creates a new <see cref="UnitConverter"/> instance.
         /// </summary>