Revive (or move) all remaining unit tests from tests_legacy

[cbjeukendrup]

Revived four ones that seemed doable, and updated the reference files in separate commits. I must say I have not made huge efforts to verify that every change to the reference files is correct, but about 90%+ I feel quite confident that it's correct. There are a couple of strange ones with huge diffs though. Anyway, since the changes are in separate commits, viewing those diffs is as easy as possible.

Because of this uncertainty, this PR is not immensely useful for verifying that we haven't broken anything without known in the past two years. But of course it does help for preventing future breakages.

Some other tests that seemed a big amount of work were not revived yet; those are moved to better locations, where we will hopefully see them often enough to be remembered about our technical debts.