Rollup merge of #133424 - Nadrieril:guard-patterns-parsing, r=fee1-dead

Parse guard patterns

This implements the parsing of [RFC3637 Guard Patterns](https://rust-lang.github.io/rfcs/3637-guard-patterns.html) (see also [tracking issue](https://github.com/rust-lang/rust/issues/129967)). This PR is extracted from https://github.com/rust-lang/rust/pull/129996 with minor modifications.

cc `@max-niederman`

compiler/rustc_ast_lowering/src/pat.rs

@@ -114,6 +114,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             self.lower_range_end(end, e2.is_some()),
                         );
                     }
+                    // FIXME(guard_patterns): lower pattern guards to HIR
+                    PatKind::Guard(inner, _) => pattern = inner,
                     PatKind::Slice(pats) => break self.lower_pat_slice(pats),
                     PatKind::Rest => {
                         // If we reach here the `..` pattern is not semantically allowed.