Improve performance of LowerTypes renaming (bp #2024) (#2025)

* Improve performance of LowerTypes renaming (#2024)

This is done by having LowerTypes uses two RenameMaps instead of one for
each module. There is one for renaming instance paths, and one for
renaming everything within modules.

Also add some utilities:
* TargetUtils for dealing with InstanceTargets
* RenameMap.fromInstanceRenames

(cherry picked from commit 15013df6

)

* Add MiMa waiver

Co-authored-by: Jack Koenig <koenig@sifive.com>