AST refactoring: merge PatWild and PatWildMulti into one variant with a flag.
Char::from_digit signature fix
auto merge of #16306 : pnkfelix/rust/fsk-ast-refactor-PatWild, r=alexcrichton

AST refactoring: merge PatWild and PatWildMulti into one variant with a flag
auto merge of #16316 : forticulous/rust/char-Fix, r=alexcrichton

Signature for `from_digit` in `Char` wasn't using `Self` so there was no way to use this method