[DSLX:run_routines] Enable quickcheck to be exhaustive.

[cdleary]

Fixes #1715

• Add support for exhaustive directive on quickchecks, updates docs.
• Adds a bitmap view, which is helpful for looking at substrings of an overall bit vector when we're trying to populate aggregate values from an underlying bit string.
• Plumbs a filesystem factory into the run routines for purposes of testing.
• Adds Value::PopulateFrom(BitmapView) and does round trip fuzz testing on it
• Adds a warning-as-error to the OSS .bazelrc, previously you could forget to return values in a function with a stated return type without getting an error