Improve generated bytecode for Switch constructs with fall through disabled if the case block returns a value

[mkouba]

Currently, the generated bytecode contains some garbage as described in quarkusio/quarkus#36626 (comment).

We could try to detect that the case block ends with a return operation and do not break the scope.

[Ladicek]

This is a very naive approach (javac seems to do a much more involved control flow analysis), but it should be good enough for a decent number of cases, so +1.