[Concurrency] Infer protocol isolation from superclass requirements.

[hborla]

Actor isolation on protocols was already inferred from inherited protocols, but we were missing inference from a required superclass.

Note that this is staged in behind the GlobalActorIsolatedTypesUsability upcoming feature, just like inference from refined protocols, because it's source breaking.

Resolves: #63473, rdar://127152935

[hborla]

@swift-ci please smoke test

[ktoso]

Looks good I think

[slavapestov]

Is there any possibility of an infinite loop with the pointless but sometimes-written

protocol P : C {}
class C : P {}