Move DateTime to shared partition (dotnet/coreclr#10460)

* Move DateTime to shared partition

Depends on #17484

* Use CoreCLR specific impl of UtcNow on windows

* Use the internal call on unix as well

* Port good corert changes

Signed-off-by: dotnet-bot-corefx-mirror <[email protected]>

Author: alexperovich

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

@@ -108,6 +108,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\ComponentModel\EditorBrowsableAttribute.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\Convert.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\DataMisalignedException.cs"/>
+    <Compile Include="$(MSBuildThisFileDirectory)System\DateTime.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\DateTimeKind.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\DayOfWeek.cs"/>
     <Compile Include="$(MSBuildThisFileDirectory)System\DBNull.cs"/>