[Authoring] Support for a default WinRT.Host.runtimeconfig

[j0shuams]

Describe the bug
Have C#/WinRT authored components generate their own runtimeconfig file and have it copied out to project/package references. Also add a property that allows authors to disable this behavior, and trust them to handle it.

Child task of #663

[j0shuams]

From my investigation, ProjectReferences might not be able to get this support because the runtimeconfig is generated later in the build, and is not available as an item to set as Content at the top-level, which is how we support the dlls flowing. For package reference we can put this runtimeconfig in the package and then have it be copied out just like the DLLs.

[j0shuams]

Done in #765