Rollup merge of #140746 - dianne:guard-pat-res, r=oli-obk

name resolution for guard patterns

This PR provides an initial implementation of name resolution for guard patterns [(RFC 3637)](https://github.com/rust-lang/rfcs/blob/master/text/3637-guard-patterns.md). This does not change the requirement that the bindings on either side of an or-pattern must be the same [(proposal here)](https://github.com/rust-lang/rfcs/blob/master/text/3637-guard-patterns.md#allowing-mismatching-bindings-when-possible); the code that handles that is separate from what this PR touches, so I'm saving it for a follow-up.

On a technical level, this separates "collecting the bindings in a pattern" (which was already done for or-patterns) from "introducing those bindings into scope". I believe the approach used here can be extended straightforwardly in the future to work with `if let` guard patterns, but I haven't tried it myself since we don't allow those yet.

Tracking issue for guard patterns: #129967

cc ``@Nadrieril``

compiler/rustc_ast/src/ast.rs

@@ -610,7 +610,7 @@ impl Pat {
     /// Walk top-down and call `it` in each place where a pattern occurs
     /// starting with the root pattern `walk` is called on. If `it` returns
     /// false then we will descend no further but siblings will be processed.
-    pub fn walk(&self, it: &mut impl FnMut(&Pat) -> bool) {
+    pub fn walk<'ast>(&'ast self, it: &mut impl FnMut(&'ast Pat) -> bool) {
         if !it(self) {
             return;
         }