Integrate verbose logging with get_sources (#3749)

Currently the verbose logging for "Sources to be formatted" is a little
suspect in that it is a completely different code path from
`get_sources`.

This can result in bugs like https://github.com/psf/black/pull/3216#issuecomment-1213557359
and generally limits the value of these logs.

This does change the "when" of this log, but the colours help separate
it from the even more verbose logs.