Rename 'compare$Type' to '$Type::compare'

As of #1427, 'map' and 'set' are also searching for an implicit 'compare' function.

After #1435 is merged, it might be a good idea to rename all 'compare$Type' functions to '$Type::compare' so that nobody needs to pass an explicit compare function anymore for the common cases at least :)
That said, this will likely be a non-trivial breakage in the community build, so whoever does this also needs to prepare the PRs there.

Beware: do _not_ rename the 'genericCompare' function :)

Start by reviewing issues #1427 and #1435, then locate all compare$Type functions and verify which references require renaming. Keep genericCompare unchanged, update the affected community-build PRs, and confirm that common map and set cases no longer need explicit compare functions.

Written by the indexing model from the issue text.