Fix for #24552 (see testcase T24552)

Fixes for a bug in desugaring pattern synonyms matches, introduced
while working on  on expanding `do`-blocks in #18324

The `matchWrapper` unecessarily (and incorrectly) filtered out the
default wild patterns in a match. Now the wild pattern alternative is
simply ignored by the pm check as its origin is `Generated`.
The current code now matches the expected semantics according to the language spec.