Lint request: warn when variable declared in match pattern shadows other variable

[PieterPenninckx]

"The Book" (TRPL) warns about variables declared in match patterns shadowing other variables. I have once been hit by this myself, so this seems to be a good idea for a lint.

[ojeda]

This was closed because the existing shadow_* lints catch it, but those lints catch also other many cases at the same time. It would be nice to have a lint only for match. Please see #3433.