Improvements to the component dependency resolution tests (dotnet/core-setup#6760)

Improvements to the component dependency resolution tests (dotnet/core-setup#6760)

* Move these under the DependencyResolution (since they belong there)
* Refactor to avoid code duplication
* Change it to not use published real builds of components, but instead simply create mocks on disk (the tests never actually run the components)
* Change where the tests put files on disk
* Reduce file copying for tests which don't need to modify the prepared components
* Delete test assets which are not used anymore

Commit migrated from https://github.com/dotnet/core-setup/commit/bba327461e7521b640be91127309760a18f12416