Fix write-back rules for Set toList

[treeowl]

• Thanks to GHC Trac ticket 16261, matching on [] in a rule LHS is pretty dicy. Generalize the write-back rules so we don't have to.

• NOINLINE set-to-list conversions generally when fusion doesn't happen. Inlining these functions seems rather unlikely to be productive in general.

[m-renaud]

~Note that as of 7 hours ago the ticket was updated and the reporter inadvertently had the overloaded lists extension enabled. Do, this appears to perennially not be an issue (?) unless I'm reading it wrong.~

[m-renaud]

Haha, I just realized you were the one who reporter it 😅

[treeowl]

Yes. I think it's likely that we should make this change anyway, to get write-back for appends, but the comment definitely needs to be fixed!

[sjakobi]

@treeowl Assigning to you, and marking as a draft (not ready for review) to clarify the current status.