fix(es/minifier): Fix variable declaration in default branch (#9220)

**Description:**

When a default branch appears before an exact match, the variable declaration should be recorded before deleting the default branch.

**Related issue:**

 - Closes #8919

Author: CPunisher

crates/swc_ecma_minifier/src/compress/optimize/switches.rs

@@ -86,7 +86,14 @@ impl Optimizer<'_> {
 
             if !may_match_other_than_exact {
                 // remove default if there's an exact match
-                cases.retain(|case| case.test.is_some());
+                cases.retain(|case| {
+                    if case.test.is_some() {
+                        true
+                    } else {
+                        var_ids.extend(case.cons.extract_var_ids());
+                        false
+                    }
+                });
             }
 
             if cases.len() == 2 {

crates/swc_ecma_minifier/tests/fixture/issues/8919/input.js

@@ -0,0 +1,11 @@
+"use strict";
+const k = (() => {
+    switch ("") {
+        default:
+            var x;
+        case "":
+            x;
+    }
+    return x;
+})();
+console.log(k);

crates/swc_ecma_minifier/tests/fixture/issues/8919/output.js

@@ -0,0 +1,2 @@
+"use strict";
+console.log(void 0);