CFE spuriously reports some non-recursive representation types as self-dependency

[chloestefantsova]

Consider the following program.

extension type E1<X>(X it) {}
typedef F<X> = X;
extension type E2<X>(E1<F<E1<X>>> it) {}

The CFE emits the following compile-time error, even though the type doesn't depend on itself.

/tmp/maybe.dart:3:22: Error: An extension type can't depend on itself through its representation type.
extension type E2<X>(E1<F<E1<X>>> it) {}
                     ^
/tmp/maybe.dart:1:16: Context: The issue arises via this extension type declaration.
extension type E1<X>(X it) {}
               ^^
/tmp/maybe.dart:2:9: Context: The issue arises via this type alias.
typedef F<X> = X;
        ^