Rollup merge of rust-lang#114070 - blyxyas:iter_mut_symbol, r=oli-obk

Add `sym::iter_mut` + `sym::as_mut_ptr` for Clippy

We currently have `sym::iter` and `sym::iter_repeat`, this PR adds `sym::iter_mut` as it's useful for rust-lang/rust-clippy#11038 and another Clippy lint, it also adds `sym::as_mut_ptr` as it's useful for rust-lang/rust-clippy#10962.

clippy_lints/src/methods/bytecount.rs

@@ -45,7 +45,7 @@ pub(super) fn check<'tcx>(
             let haystack = if let ExprKind::MethodCall(path, receiver, [], _) =
                     filter_recv.kind {
                 let p = path.ident.name;
-                if p == sym::iter || p == sym!(iter_mut) {
+                if p == sym::iter || p == sym::iter_mut {
                     receiver
                 } else {
                     filter_recv