Move String to shared corelib partition (dotnet/coreclr#16749)

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

Author: jkotas

src/Common/src/CoreLib/Interop/Windows/Kernel32/Interop.MultiByteToWideChar.cs

@@ -0,0 +1,20 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Runtime.InteropServices;
+
+internal partial class Interop
+{
+    internal partial class Kernel32
+    {
+        [DllImport(Libraries.Kernel32)]
+        internal static extern unsafe int MultiByteToWideChar(
+            uint CodePage, uint dwFlags,
+            byte* lpMultiByteStr, int cbMultiByte,
+            char* lpWideCharStr, int cchWideChar);
+
+        internal const uint MB_PRECOMPOSED = 0x00000001;
+    }
+}

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

@@ -492,6 +492,7 @@
     <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.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\String.Manipulation.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\String.Searching.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\StackOverflowException.cs" />
@@ -686,6 +687,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.Globalization.cs" Condition="'$(EnableDummyGlobalizationImplementation)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.LockFile.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.MAX_PATH.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.MultiByteToWideChar.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.OutputDebugString.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.ReadFile_SafeHandle_IntPtr.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Interop\Windows\Kernel32\Interop.ReadFile_SafeHandle_NativeOverlapped.cs" />