Pulling in CoreFX changes and fixing up Sse2.StoreLow to be Sse2.StoreScalar (#24123)
* Update dependencies from https://github.com/dotnet/corefx build
20190419.5
- Microsoft.NETCore.Platforms - 3.0.0-preview5.19219.5
- Microsoft.Private.CoreFx.NETCoreApp - 4.6.0-preview5.19219.5
* Removing the Sse2.StoreLow(long/ulong*, ...) methods that have been replaced
* Moving the Sse2.StoreLow(long/ulong*, ...) tests to be Sse2.StoreScalar tests
* Fixing some existing usages of Sse2.StoreLow(long/ulong*, ...)
Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>