[Analyzer] Improve error message when extension type is not well-bounded

[sgrekhov]

Based on the dart-lang/co19#2384 (comment) and #54097 (comment), please, improve analyzer error messafe in case of

extension type V<T extends V<T>>(T id) {}

The current message

COMPILE_TIME_ERROR.TYPE_PARAMETER_SUPERTYPE_OF_ITS_BOUND
'T' can't be a supertype of its upper bound.

is not much helpfull in this case