[JS IR] IC improvements

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

js/js.translator/testData/incremental/invalidation/privateInlineFunction1/lib2/module.info

@@ -1,7 +1,5 @@
 STEP 0:
     dependencies: stdlib, lib1
     dirty: l2.kt
-
 STEP 1:
     dependencies: stdlib, lib1
-    dirty:

js/js.translator/testData/incremental/invalidation/privateInlineFunction1/main/m.kt

@@ -1,2 +1,9 @@
 
-fun box() = qux(4, 2)
+fun box(stepId: Int): String {
+    when (stepId) {
+        0 -> if (qux(4, 2) != -8) return "Fail"
+        1 -> if (qux(4, 2) != -4) return "Fail"
+        else -> return "Unknown"
+    }
+    return "OK"
+}

js/js.translator/testData/incremental/invalidation/privateInlineFunction1/main/module.info

@@ -1,7 +1,5 @@
 STEP 0:
     dependencies: stdlib, lib1, lib2
     dirty: m.kt
-
 STEP 1:
     dependencies: stdlib, lib1, lib2
-    dirty:

js/js.translator/testData/incremental/invalidation/privateInlineFunction1/project.info

@@ -2,6 +2,7 @@ MODULES: lib1, lib2, main
 
 STEP 0:
     libs: lib1, lib2, main
-
+    dirty js: stdlib, lib1, lib2, main
 STEP 1:
-    libs: lib1, lib2, main
+    libs: lib1, lib2, main
+    dirty js: lib1