[master] Update dependencies from dotnet/corefx (dotnet/coreclr#25807)

[master] Update dependencies from dotnet/corefx (dotnet/coreclr#25807)

* Update dependencies from https://github.com/dotnet/corefx build 20190719.9

- Microsoft.NETCore.Platforms - 5.0.0-alpha1.19369.9
- Microsoft.Private.CoreFx.NETCoreApp - 5.0.0-alpha1.19369.9

* Update dependencies from https://github.com/dotnet/corefx build 20190720.5

- Microsoft.NETCore.Platforms - 5.0.0-alpha1.19370.5
- Microsoft.Private.CoreFx.NETCoreApp - 5.0.0-alpha1.19370.5

* Update dependencies from https://github.com/dotnet/corefx build 20190721.2

- Microsoft.NETCore.Platforms - 5.0.0-alpha1.19371.2
- Microsoft.Private.CoreFx.NETCoreApp - 5.0.0-alpha1.19371.2

Commit migrated from https://github.com/dotnet/coreclr/commit/fadee1275f3722a11bd37b8c03d80fd748bd025d