Rollup merge of #130635 - eholk:pin-reborrow-sugar, r=compiler-errors

Add `&pin (mut|const) T` type position sugar

This adds parser support for `&pin mut T` and `&pin const T` references. These are desugared to `Pin<&mut T>` and `Pin<&T>` in the AST lowering phases.

This PR currently includes #130526 since that one is in the commit queue. Only the most recent commits (bd450027eb4a94b814a7dd9c0fa29102e6361149 and following) are new.

Tracking:

- #130494

r? `@compiler-errors`

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1163,6 +1163,12 @@ impl<'a> State<'a> {
                 self.print_opt_lifetime(lifetime);
                 self.print_mt(mt, false);
             }
+            ast::TyKind::PinnedRef(lifetime, mt) => {
+                self.word("&");
+                self.print_opt_lifetime(lifetime);
+                self.word("pin ");
+                self.print_mt(mt, true);
+            }
             ast::TyKind::Never => {
                 self.word("!");
             }