Decompiler improvements meta

[tlringer]

Needs triaging into issues. Some ideas to refer to as RanDair continues his work:

1. Custom tactics & decision procedures (WIP)
2. Comment & format preservaton
3. Removing additional arguments to apply and rewrite
4. Looking directly at old tactic scripts instead of just taking tactics as arguments
5. Improving performance
6. Custom tactics that aren't decision procedures (especially non-solving tactics)

Blocked by current work on (1) right now.