test: add edge case coverage for Array.prototype.find (#5221)

I added test cases for Array.prototype.find covering edge cases that 
weren't tested before:

- Empty array returns undefined
- No match returns undefined
- Returns first match not last
- Works correctly with objects
- Callback receives correct index
- Sparse array holes are visited

No existing tests were removed or modified.

Author: ParthMozarkar

core/engine/src/builtins/array/tests.rs

@@ -962,3 +962,26 @@ fn array_of_neg_zero() {
         TestAction::assert("arr.every(x => (1/x) === -Infinity)"),
     ]);
 }
+
+#[test]
+fn array_prototype_find_edge_cases() {
+    run_test_actions([
+        TestAction::run_harness(),
+        TestAction::assert("[].find(x => x === 1) === undefined"),
+        TestAction::assert("[1, 2, 3].find(x => x === 99) === undefined"),
+        TestAction::assert("[1, 2, 1].find(x => x === 1) === 1"),
+        TestAction::assert(indoc! {r#"
+            var obj = { name: "Alice" };
+            [obj].find(x => x.name === "Alice") === obj
+        "#}),
+        TestAction::assert(indoc! {r#"
+            var idx = -1;
+            [10, 20, 30].find((v, i) => { idx = i; return v === 20; });
+            idx === 1
+        "#}),
+        TestAction::assert(indoc! {r#"
+            let arr = [1, , 3];
+            arr.find(x => x === undefined) === undefined
+        "#}),
+    ]);
+}