Support GADT reasoning over path-dependent types

[Linyxus]

This PR enables GADT reasoning over path-dependent types. Specifically, it adds to the GadtConstraint the functionality to register path-dependent types and record bounds for them.

The following code will not type-check before this PR:

trait Expr[+T]
case class LitInt(x: Int) extends Expr[Int]

trait Tag { type T }

def f(p: Tag, e: Expr[p.T]): p.T = e match
  case LitInt(x) => x

Note that this PR does not add handling for type member reasoning in pattern matching. This will be added in a future PR.

[Linyxus]

test performance please

[dottybot]

performance test scheduled: 7 job(s) in queue, 1 running.

[dottybot]

Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/13364/ to see the changes.

Benchmarks is based on merging with master (dd7a07a)

[Linyxus]

test performance please

[Linyxus]

Working directly on the full support (in #13475)!