Use file name whitelist to prevent RCE

Summary:
Use a whitelist to validate user-provided file names. This doesn't cover the entire range of valid filenames but should cover almost all of them in practice. Allows letters, numbers, periods, dashes, and underscores. Opting to use a whitelist instead of a blacklist because getting this wrong leaves us vulnerable to a RCE attack.

This is the same patch I submitted to create-react-app: https://github.com/facebook/create-react-app/pull/4866

See s163726 for more details

Reviewed By: LukasReschke

Differential Revision: D9504148

fbshipit-source-id: e3c7587f1b7f93bec90a58a38d5f6d58f1f59275