Improving the Simplifier
This MR addresses #23745 (closed) and #23627 (closed). It is really just a collection of tweaks to the Simplifier, but it seems to give good compile-time improvements.
It has three commits: one large, two small.
Currently it is rebased on top of !9614 (merged), which is now in Marge's hands. As soon as that lands I can rebase it on master. But meanwhile just ignore changes to
- The occurrence analysers
- The JoinPointHood data type