Auto merge of #68376 - Centril:move-ref-patterns, r=matthewjasper

Initial implementation of `#![feature(move_ref_pattern)]`

Following up on #45600, under the gate `#![feature(move_ref_pattern)]`, `(ref x, mut y)` is allowed subject to restrictions necessary for soundness. The match checking implementation and tests for `#![feature(bindings_after_at)]` is also adjusted as necessary.

Closes #45600.
Tracking issue: #68354.

r? @matthewjasper

src/test/ui/error-codes/E0009.rs

@@ -1,9 +0,0 @@
-fn main() {
-    struct X { x: (), }
-    let x = Some((X { x: () }, X { x: () }));
-    match x {
-        Some((y, ref z)) => {},
-        //~^ ERROR E0009
-        None => panic!()
-    }
-}

src/test/ui/error-codes/E0009.stderr

@@ -1,11 +0,0 @@
-error[E0009]: cannot bind by-move and by-ref in the same pattern
-  --> $DIR/E0009.rs:5:15
-   |
-LL |         Some((y, ref z)) => {},
-   |               ^  ----- by-ref pattern here
-   |               |
-   |               by-move pattern here
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0009`.