Add MemoryExtensions to CoreLib along with necessary SpanHelpers (#16521)

* Add MemoryExtensions to CoreLib along with necessary SpanHelpers

* Make the newly added AsSpan/AsMemory into array extension methods.

* Remove StringSpanHelpers.Trim

* Leftover AsReadOnlySpan -> AsSpan for *Unix.cs files

* Address PR feedback.

* Remove duplicate methods in the Span class.

* Temporarily disable AsBytes SpanBench test.

* Add back AsBytes

* Re-enable AsBytes SpanBench test

Signed-off-by: dotnet-bot-corefx-mirror <dotnet-bot@microsoft.com>

Author: ahsonkhan

src/Common/src/CoreLib/System.Private.CoreLib.Shared.projitems

@@ -241,6 +241,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\MemberAccessException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Memory.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\MemoryDebugView.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\MemoryExtensions.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\MemoryExtensions.Fast.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\MethodAccessException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\MidpointRounding.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\MissingMethodException.cs" />
@@ -485,8 +487,12 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Single.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Span.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Span.Fast.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\SpanDebugView.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Span.NonGeneric.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\SpanDebugView.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\SpanHelpers.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\SpanHelpers.BinarySearch.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\SpanHelpers.Byte.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\SpanHelpers.T.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\String.Manipulation.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\String.Searching.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\StringSpanHelpers.cs" />

src/Common/src/CoreLib/System/Double.cs

@@ -345,7 +345,7 @@ private static bool TryParse(ReadOnlySpan<char> s, NumberStyles style, NumberFor
             bool success = Number.TryParseDouble(s, style, info, out result);
             if (!success)
             {
-                ReadOnlySpan<char> sTrim = StringSpanHelpers.Trim(s);
+                ReadOnlySpan<char> sTrim = s.Trim();
                 if (StringSpanHelpers.Equals(sTrim, info.PositiveInfinitySymbol))
                 {
                     result = PositiveInfinity;

src/Common/src/CoreLib/System/MemoryExtensions.Fast.cs

@@ -162,11 +162,11 @@ public void Clear()
         {
             if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
             {
-                Span.ClearWithReferences(ref Unsafe.As<T, IntPtr>(ref _pointer.Value), (nuint)_length * (nuint)(Unsafe.SizeOf<T>() / sizeof(nuint)));
+                SpanHelpers.ClearWithReferences(ref Unsafe.As<T, IntPtr>(ref _pointer.Value), (nuint)_length * (nuint)(Unsafe.SizeOf<T>() / sizeof(nuint)));
             }
             else
             {
-                Span.ClearWithoutReferences(ref Unsafe.As<T, byte>(ref _pointer.Value), (nuint)_length * (nuint)Unsafe.SizeOf<T>());
+                SpanHelpers.ClearWithoutReferences(ref Unsafe.As<T, byte>(ref _pointer.Value), (nuint)_length * (nuint)Unsafe.SizeOf<T>());
             }
         }