[Concurrency] isolated fixes; ban Array<T> and handle Self in actor

[ktoso]

This fixes two logic isolated issues:

Seems to have been present for a long time:

• Due to a typo in the logic "is" vs "has" TypeParameter we allowed Array which doesn't make sense.

Recent, due to #70925 being too permissive in Self handling:

• Technically self in an actor is handled like self in classess... so @slavapestov explained that we need to handle the following differently:

// TODO: Consider making an actor's Self behave like in a struct, removing this special casing.
//       We could consider changing this, so that self is always Self because we don't allow inheritance of actors.
//       See: https://github.com/apple/swift/issues/70954 and rdar://121091417
actor A2 {
  nonisolated func f1() async {
    await { (self: isolated Self) in }(self)
    // expected-error@-1 {{cannot convert value of type 'A2' to expected argument type 'Self'}}
  }
  nonisolated func f2() async -> Self {
    await { (self: isolated Self) in }(self)
    return self
  }
}

[ktoso]

@swift-ci please smoke test

[hborla]

I think this needs to happen after unwrapping the optional below, otherwise we will not allow isolated Self?. We do generally allow optional Self as a special case to the covariant Self restrictions.

[ktoso]

Nice catch, fixing that -- and added tests

[ktoso]

@swift-ci please smoke test