[JS IR] Improve stepping test executor

Don't search for box function in the generated code;
instead, stop the execution right before calling it.

This makes stepping tests more accurate.

compiler/testData/debug/stepping/nestedInline.kt

@@ -65,5 +65,12 @@ inline fun html(init: () -> Unit) {
 // test.kt:21 box
 
 // EXPECTATIONS JS_IR
+// test.kt:7 box
+// 1.kt:33 box
+// 1.kt:36 box
+// 1.kt:37 box
+// 1.kt:37 box
+// 1.kt:41 box
+// test.kt:15 box
 // test.kt:19 box
 // test.kt:21 box