fix(es/minifier): Use UTF16 length for str.length (#7275)

**Related issue:**

 - Closes #7274.

Author: kdy1

crates/swc_ecma_minifier/tests/exec.rs

@@ -10931,3 +10931,22 @@ fn issue_6914_3() {
         false,
     );
 }
+
+#[test]
+fn issue_7274() {
+    run_default_exec_test(
+        r###"
+        if (
+            // incorrect:
+            "😋📋👌".length === 3
+    
+            // correct:
+            // "😋📋👌".length === 6
+        ) {
+            // side effect
+            new Response(123);
+        }
+        console.log('PASS');
+        "###,
+    );
+}

crates/swc_ecma_transforms_optimization/src/simplify/expr/mod.rs

@@ -154,7 +154,7 @@ impl SimplifyExpr {
                     self.changed = true;
 
                     *expr = Expr::Lit(Lit::Num(Number {
-                        value: value.chars().count() as f64,
+                        value: value.chars().map(|c| c.len_utf16()).sum::<usize>() as _,
                         span: *span,
                         raw: None,
                     }));