Better Pass Infrastructure

[acl-cqc]

At present we have a bunch of things that call themselves Passes - ConstantFoldPass, MonomorphizePass, RemoveDeadFuncsPass.

Each of these has its own copy of code to allow setting a ValidationLevel, and some have other pass-specific configuration. There is no common interface - the idea of a "pass" is purely conceptual. They then run via ValidationLevel::run_validated_pass with a callback (leading to quite a complicated signature, and possibly fun with the borrow-checker).

We could improve on this via:

• A trait Pass which could be roughly, fn run(h: &mut impl HugrMut) -> Result<(), Self::Error> (plus associated type Error)
• A ValidatingPass<P: Pass>(P, ValidationLevel) that wraps another pass with something like the current ValidationLevel but without ValidationLevel::None. We could have a single ValidationPassError<E> that reports either an error in validation (before/after) or an underlying error E
• Some kind of "SequencePass" that wraps a bunch of other passes (I think this would have to use dyn so maybe just two arbitrary passes) - and we can add methods to trait Pass that combine Passes e.g. and_then(other: impl Pass) -> impl Pass. This would combine with the previous to allow validation before/after a number of passes but not at steps inbetween.
• Maybe common config for specifying inputs, reachable functions, anything else - e.g. constant folding: FuncDefns and FuncDecls are not considered needed #1797 / Decide on which functions are "public" #1752