Selectively revert 36683a804c to resolve
a source compatibility regression. See inline comment for use case. We
are going to consider acknowledging this use case in the rules in a
future release.
The non-metatype case was never supported. The same should hold for the
existential metatype case, which used to miscompile and now crashes
because the invariant reference is deemed OK but the erasure expectedly
fails to handle it:
```swift
class C<T> {}
protocol P {
associatedtype A
func f() -> any P & C<A>
func fMeta() -> any (P & C<A>).Type
}
do {
let p: any P
let _ = p.f() // error
let _ = p.fMeta() // crash
}
```
