Expose both v1 and v1alpha reflection services

[jhump]

Resolves #5684.

This adds RegisterV1 and RegisterV1Alpha to provide control over the versions registered. The existing Register function registers both versions.

This also adds NewServerV1 to return a server that implements the new version. NewServer continues to return the v1alpha version of the interface.

All of the core logic and types have been updated to refer to the newer definitions in v1. Adapters have been added, to convert between v1 and v1alpha, to provide the v1alpha server. The adapters are also used in tests, so that the end-to-end tests now go through both v1 and v1alpha stubs, to verify both versions work correctly.

[jhump]

@dfawley, sorry for not waiting for an answer to my question on #5684. I guess I was optimistic that maybe you'd accept a pull request for it. Let me know what you think.