Bundle sever should react to changes in any in-repo dependency

[afoxman]

When a metro server is running, it should react to changes in any dependent package in the repo, not just the app package.

Make sure that typescript validation is happening on these dependencies -- specifically, on the source .ts[x] files.

Originally posted by @afoxman in https://github.com/microsoft/rnx-kit/issues/173#issuecomment-829501383

[afoxman]

I think the babel path remapper we have will make this possible.

[tido64]

Metro should already be watching everything, particularly because it can only resolve files that are being watched.