Add a test to prevent regressions

The MetadataLoadContext should work on Browser, but the test requires
better MetadataAssemblyResolver implementation

System.Runtime still fails to resolve on Browser.
WinMD parsing on Browser is questionable enough. Though, with better
MetadataAssemblyResolver impl it should still work. Making this new
unit test be Browser-aware is out-of-scope for this fix.
The issue to be fixed is not related to assembly loading at all.