[master] Update dependencies from 4 repositories (dotnet/corefx#41216)

[master] Update dependencies from 4 repositories (dotnet/corefx#41216)

* Update global.json

* Disable DependentUpon convention for resources

* Update dependencies from https://github.com/dotnet/core-setup build 20190920.7

- Microsoft.NETCore.App - 5.0.0-alpha1.19470.7
- Microsoft.NETCore.DotNetHostPolicy - 5.0.0-alpha1.19470.7
- Microsoft.NETCore.DotNetHost - 5.0.0-alpha1.19470.7

* Update dependencies from https://github.com/dotnet/corefx build 20190921.2

- runtime.native.System.IO.Ports - 5.0.0-alpha1.19471.2
- Microsoft.NETCore.Platforms - 5.0.0-alpha1.19471.2

* Cleanup netcoreapp targeting pack restore

For .NETCore2x the SDK implictily references the targeting pack via
a PackageReference so to binplace the assemblies we just need to reset
the PrivateAssets and IsImplicitlyDefined attributes.

For .NETCore >= 3 we don't need to reset any attributes on the
FrameworkReference.

We default to the version that is bundled within the SDK in the
Microsoft.NETCoreSdk.BundledVersions.props file.

* Update dependencies from https://github.com/dotnet/standard build 20190922.1

- NETStandard.Library - 2.2.0-prerelease.19472.1

* Update SDK to 3.0.100 stable

* Simplify code in netcoreapp.depproj

* Update packageIndex inbox matrix for S.R.Emit

* Manual darc update from build '20190923.5'

Commit migrated from https://github.com/dotnet/corefx/commit/90f7cc01418c059f496528beeca77c5f5549e6fc