Adding docs for Unsafe Apis in System.Runtime.CompilerServices (#2819)

* adding docs

* summary on one line and comppare -> compare

* adding specified prefix

Co-Authored-By: Maira Wenzel <mairaw@microsoft.com>

Author: Anipik

xml/System.Runtime.CompilerServices/Unsafe.xml

@@ -49,11 +49,11 @@
         <Parameter Name="elementOffset" Type="System.Int32" Index="1" FrameworkAlternate="dotnet-plat-ext-2.1;dotnet-plat-ext-2.2;netcore-3.0" />
       </Parameters>
       <Docs>
-        <typeparam name="T">To be added.</typeparam>
-        <param name="source">To be added.</param>
-        <param name="elementOffset">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <typeparam name="T">The type of void pointer.</typeparam>
+        <param name="source">The void pointer to add the offset to.</param>
+        <param name="elementOffset">The offset to add.</param>
+        <summary>Adds an element offset to the given void pointer.</summary>
+        <returns>A new void pointer that reflects the addition of offset to the specified pointer.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -185,9 +185,7 @@
         <typeparam name="T">The type of reference.</typeparam>
         <param name="left">The first reference to compare.</param>
         <param name="right">The second reference to compare.</param>
-        <summary>
-          Determines whether the specified references point to the same location.
-        </summary>
+        <summary>Determines whether the specified references point to the same location.</summary>
         <returns>
           <see langword="true" /> if <paramref name="left" /> and <paramref name="right" /> point to the same location; otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>
@@ -764,11 +762,11 @@
         <Parameter Name="right" Type="T" RefType="ref" Index="1" FrameworkAlternate="dotnet-plat-ext-2.1;dotnet-plat-ext-2.2;netcore-3.0" />
       </Parameters>
       <Docs>
-        <typeparam name="T">To be added.</typeparam>
-        <param name="left">To be added.</param>
-        <param name="right">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <typeparam name="T">The type of the reference.</typeparam>
+        <param name="left">The first value to compare.</param>
+        <param name="right">The second value to compare.</param>
+        <summary>Returns a value that indicates whether a specified reference is greater than another specified reference.</summary>
+        <returns><see langword="true" /> if <paramref name="left" /> is greater than <paramref name="right" />; otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -797,11 +795,11 @@
         <Parameter Name="right" Type="T" RefType="ref" Index="1" FrameworkAlternate="dotnet-plat-ext-2.1;dotnet-plat-ext-2.2;netcore-3.0" />
       </Parameters>
       <Docs>
-        <typeparam name="T">To be added.</typeparam>
-        <param name="left">To be added.</param>
-        <param name="right">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <typeparam name="T">The type of the reference.</typeparam>
+        <param name="left">The first value to compare.</param>
+        <param name="right">The second value to compare.</param>
+        <summary>Returns a value that indicates whether a specified reference is less than another specified reference.</summary>
+        <returns><see langword="true" /> if <paramref name="left" /> is less than <paramref name="right" />; otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -964,11 +962,11 @@
         <Parameter Name="elementOffset" Type="System.Int32" Index="1" FrameworkAlternate="dotnet-plat-ext-2.1;dotnet-plat-ext-2.2;netcore-3.0" />
       </Parameters>
       <Docs>
-        <typeparam name="T">To be added.</typeparam>
-        <param name="source">To be added.</param>
-        <param name="elementOffset">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <typeparam name="T">The type of the void pointer.</typeparam>
+        <param name="source">The void pointer to subtract the offset from.</param>
+        <param name="elementOffset">The offset to subtract.</param>
+        <summary>Subtracts an element offset from the given void pointer.</summary>
+        <returns>A new void pointer that reflects the subtraction of offset from the specified pointer.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1062,8 +1060,7 @@
       <Docs>
         <typeparam name="T">The type of reference.</typeparam>
         <param name="source">The reference to subtract the offset from.</param>
-        <param name="bytesOffset">The offset to subtract.</param>
-        <param name="byteOffset">To be added.</param>
+        <param name="byteOffset">The offset to subtract.</param>
         <summary>
         Subtracts a byte offset from the given reference.
         </summary>