Rollup merge of rust-lang#140981 - est31:guard_let_chains_tests, r=petrochenkov

Add match guard let chain drop order and scoping tests

We have a bunch of tests for if let chain drop order, but those tests don't cover match guard chains to the same depth. This PR adds the following tests:

* match guard equivalents of the if let chains tests in the `drop-order-comparisons.rs` test, added by  rust-lang#133605.
* match guard equivalent of the `mir_let_chains_drop_order.rs` test, added by rust-lang#107251
* match guard equivalent of `temporary-early-drop.rs`, added by rust-lang#133093

The added tests all have variants for 2021 and 2024, showing that the behavior on both editions matches that of if let chains on 2024.

tracking issue: rust-lang#51114

Author: matthiaskrgr

tests/ui/drop/drop-order-comparisons.e2021.fixed

@@ -24,6 +24,7 @@
 //@ [e2024] edition: 2024
 //@ run-pass
 
+#![feature(if_let_guard)]
 #![cfg_attr(e2021, feature(let_chains))]
 #![cfg_attr(e2021, warn(rust_2024_compatibility))]
 
@@ -344,6 +345,25 @@ fn t_if_let_chains_then() {
     e.assert(9);
 }
 
+#[rustfmt::skip]
+fn t_guard_if_let_chains_then() {
+    let e = Events::new();
+    _ = match () {
+        () if e.ok(1).is_ok()
+            && let true = e.ok(9).is_ok()
+            && let Ok(_v) = e.ok(8)
+            && let Ok(_) = e.ok(7)
+            && let Ok(_) = e.ok(6).as_ref()
+            && e.ok(2).is_ok()
+            && let Ok(_v) = e.ok(5)
+            && let Ok(_) = e.ok(4).as_ref() => {
+                e.mark(3);
+            }
+        _ => {}
+    };
+    e.assert(9);
+}
+
 #[cfg(e2021)]
 #[rustfmt::skip]
 fn t_if_let_nested_else() {
@@ -484,6 +504,25 @@ fn t_if_let_chains_then_else() {
     e.assert(9);
 }
 
+#[rustfmt::skip]
+fn t_guard_if_let_chains_then_else() {
+    let e = Events::new();
+    _ = match () {
+       () if e.ok(1).is_ok()
+            && let true = e.ok(8).is_ok()
+            && let Ok(_v) = e.ok(7)
+            && let Ok(_) = e.ok(6)
+            && let Ok(_) = e.ok(5).as_ref()
+            && e.ok(2).is_ok()
+            && let Ok(_v) = e.ok(4)
+            && let Ok(_) = e.err(3) => {}
+        _ => {
+            e.mark(9);
+        }
+    };
+    e.assert(9);
+}
+
 fn main() {
     t_bindings();
     t_tuples();
@@ -502,10 +541,12 @@ fn main() {
     t_if_let_nested_then();
     t_let_else_chained_then();
     t_if_let_chains_then();
+    t_guard_if_let_chains_then();
     t_if_let_nested_else();
     t_if_let_nested_then_else();
     t_let_else_chained_then_else();
     t_if_let_chains_then_else();
+    t_guard_if_let_chains_then_else();
 }
 
 // # Test scaffolding