[JS IR] IC improvements

- Reuse a built fragment
  - Use cache for saving built JS code

js/js.translator/testData/incremental/invalidation/class/main/m.kt

@@ -1,2 +1,9 @@
 
-fun box() = Demo(100500) == Demo(15)
+fun box(stepId: Int): String {
+    when (stepId) {
+        0, 2 -> if (Demo(15) == Demo(15)) return "Fail"
+        1, 3 -> if (Demo(15) != Demo(15)) return "Fail"
+        else -> return "Unknown"
+    }
+    return "OK"
+}

js/js.translator/testData/incremental/invalidation/class/main/module.info

@@ -1,9 +1,5 @@
 STEP 0:
     dependencies: stdlib, lib1
     dirty: m.kt
-STEP 1:
-    dependencies: stdlib, lib1
-STEP 2:
-    dependencies: stdlib, lib1
-STEP 3:
+STEP 1..3:
     dependencies: stdlib, lib1