Clean up terminology: step 3 — the rest of the owl

[lqd]

Completes most of The Great Renaming™ to also align:

• input relations and .facts files (borrow_region to loan_issued_at, killed to loan_killed_at, invalidates to loan_invalidated_at, outlives to subset_base)
• some of the effects in the test parser mentioning the previous input relations
• the data computed by the variants ( requires relation to origin_contains_loan_on_entry, borrow_live_at to loan_live_at) and the API accessing this data
• some debug output relations (which used the very old restricts instead of requires, now use origin_contains_loan_*)
• (also removes an unused dataset)

with the naming plan in our rules hackmd.

This PR will need require rustc's fact generation to be updated to use these new names as well.

For review purposes: since there's a lot of renaming, each commit can be reviewed individually. Note that the commits renaming the datasets' fact files are prefixed with "tests".

[nikomatsakis]

this is amazing and you are a hero. do you want me to merge this now, @lqd, or do you have a particular ordering?

[lqd]

@nikomatsakis this one was the one I planned we'd merge first :)

[nikomatsakis]

DONE