Rollup merge of #140257 - amandasystems:housecleaning, r=wesleywiser

Some drive-by housecleaning in `rustc_borrowck`

This commit picks up a few odd ends discovered during the work on #130227. It adds some documentation and renames a few methods with too generic names to describe what they actually do. It also adds some debug output that was helpful during bug hunting and generally cleans up a few things (for my values of "clean").

r? lcnr

Author: matthiaskrgr