Move Span/ReadOnlySpan to shared CoreLib partition (#10988)

Fix a few method names to better names used in CoreRT

Contributes to dotnet/corert#2966

Author: jkotas

src/mscorlib/System.Private.CoreLib.csproj

@@ -381,8 +381,6 @@
     <Compile Condition="'$(FeatureCominterop)' == 'true'" Include="$(BclSourcesRoot)\System\Variant.cs" />
     <Compile Condition="'$(FeatureClassicCominterop)' == 'true'" Include="$(BclSourcesRoot)\System\OleAutBinder.cs" />
     <Compile Include="$(BclSourcesRoot)\System\ByReference.cs" />
-    <Compile Include="$(BclSourcesRoot)\System\Span.cs" />
-    <Compile Include="$(BclSourcesRoot)\System\ReadOnlySpan.cs" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="$(BclSourcesRoot)\Internal\Runtime\Augments\EnvironmentAugments.cs" />

src/mscorlib/shared/System.Private.CoreLib.Shared.projitems

@@ -169,6 +169,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Progress.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\Random.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\RankException.cs"/>
+    <Compile Include="$(MSBuildThisFileDirectory)System\ReadOnlySpan.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\AmbiguousMatchException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\Assembly.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\AssemblyAlgorithmIdAttribute.cs" />
@@ -338,6 +339,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Security\SuppressUnmanagedCodeSecurityAttribute.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\Security\UnverifiableCodeAttribute.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\Security\VerificationException.cs"/>
+    <Compile Include="$(MSBuildThisFileDirectory)System\Span.cs"/>
+    <Compile Include="$(MSBuildThisFileDirectory)System\Span.NonGeneric.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\StackOverflowException.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\StringComparer.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\StringComparison.cs"/>

src/mscorlib/src/System/ReadOnlySpan.cs renamed to src/mscorlib/shared/System/ReadOnlySpan.cs

@@ -34,7 +34,7 @@ public ReadOnlySpan(T[] array)
             if (array == null)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
 
-            _pointer = new ByReference<T>(ref JitHelpers.GetArrayData(array));
+            _pointer = new ByReference<T>(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()));
             _length = array.Length;
         }
 
@@ -57,7 +57,7 @@ public ReadOnlySpan(T[] array, int start)
             if ((uint)start > (uint)array.Length)
                 ThrowHelper.ThrowArgumentOutOfRangeException();
 
-            _pointer = new ByReference<T>(ref Unsafe.Add(ref JitHelpers.GetArrayData(array), start));
+            _pointer = new ByReference<T>(ref Unsafe.Add(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()), start));
             _length = array.Length - start;
         }
 
@@ -81,7 +81,7 @@ public ReadOnlySpan(T[] array, int start, int length)
             if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
                 ThrowHelper.ThrowArgumentOutOfRangeException();
 
-            _pointer = new ByReference<T>(ref Unsafe.Add(ref JitHelpers.GetArrayData(array), start));
+            _pointer = new ByReference<T>(ref Unsafe.Add(ref Unsafe.As<byte, T>(ref array.GetRawSzArrayData()), start));
             _length = length;
         }
 
@@ -202,7 +202,7 @@ public bool TryCopyTo(Span<T> destination)
             if ((uint)_length > (uint)destination.Length)
                 return false;
 
-            SpanHelper.CopyTo<T>(ref destination.DangerousGetPinnableReference(), ref _pointer.Value, _length);
+            Span.CopyTo<T>(ref destination.DangerousGetPinnableReference(), ref _pointer.Value, _length);
             return true;
         }
 
@@ -301,7 +301,7 @@ public T[] ToArray()
                 return Array.Empty<T>();
 
             var destination = new T[_length];
-            SpanHelper.CopyTo<T>(ref JitHelpers.GetArrayData(destination), ref _pointer.Value, _length);
+            Span.CopyTo<T>(ref Unsafe.As<byte, T>(ref destination.GetRawSzArrayData()), ref _pointer.Value, _length);
             return destination;
         }