I thought it might be impossible to recursively lookupConformance of
Copyable, unlike for Sendable. Turns out there are still situations
where it can happen, that aren't invalid.
This alone fixes `ClangImporter/objc_bridging_generics.swift` and will
help reveal any invalid request cycles.
I thought this would be simple to add a check for this, but it turns out
that a more complete refactoring that eliminates `isNoEscape` in favor
of `isEscapable` is most likely needed.
An unbound generic type is not something that should end up in
`isNoncopyable` or `isEscapable` queries because there are no
conformances for such a type; it's unbound!
fixes test/Constraints/closures.swift
First, "can have an absence of Copyable" is a rather confusing notion,
so the query is flipped to "can be Copyable". Next, it's more robust to
ask if a conformance exists for the TypeDecl to answer that question,
rather than trying to replicate what happens within that conformance
lookup.
Also renames `TypeDecl::isEscapable` to match.
