Auto merge of #108504 - cjgillot:thir-pattern, r=compiler-errors,Nilstrieb

Check pattern refutability on THIR

The current `check_match` query is based on HIR, but partially re-lowers HIR into THIR.
This PR proposed to use the results of the `thir_body` query to check matches, instead of re-building THIR.

Most of the diagnostic changes are spans getting shorter, or commas/semicolons not getting removed.

This PR degrades the diagnostic for confusing constants in patterns (`let A = foo()` where `A` resolves to a `const A` somewhere): it does not point ot the definition of `const A` any more.

Author: bors