known bounds
Potential types from trait bounds are enumerated and, if there's no
possible coercions/unsizing, are searched for a single type that meets
all known conditions (i.e. trait bounds on the ivar, and method
existence)
but it's less ugly)
- Also includes some MIR optimisation changes to reduce some compile times (hopefully)
- Removed duplicated MIR consteval and now-unused HIR consteval