Rollup merge of #122793 - compiler-errors:deref-pat-syntax, r=Nadrieril

Implement macro-based deref!() syntax for deref patterns

Stop using `box PAT` syntax for deref patterns, and instead use a perma-unstable macro.

Blocked on #122222

r? `@Nadrieril`

compiler/rustc_passes/src/hir_stats.rs

@@ -300,6 +300,7 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
                 Path,
                 Tuple,
                 Box,
+                Deref,
                 Ref,
                 Lit,
                 Range,
@@ -566,6 +567,7 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
                 Path,
                 Tuple,
                 Box,
+                Deref,
                 Ref,
                 Lit,
                 Range,