[JS IR] IC improvements

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

js/js.translator/testData/incremental/invalidation/removeModule/lib1/module.info

@@ -1,7 +1,6 @@
 STEP 0:
     dependencies: stdlib
     dirty: l1.kt
-
 STEP 1:
     dependencies: stdlib
-    flags: FP
+    flags: FP UNUSED

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

@@ -1,9 +1,8 @@
 STEP 0:
     dependencies: stdlib, lib1
     dirty: l2.kt
-
 STEP 1:
     dependencies: stdlib
     modifications:
         U : l2.kt.1 -> l2.kt
-    dirty: l2.kt
+    dirty: l2.kt

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

@@ -1,2 +1,9 @@
 
-fun box() = qux()
+fun box(stepId: Int): String {
+    when (stepId) {
+        0 -> if (qux() != 42) return "Fail"
+        1 -> if (qux() != 99) return "Fail"
+        else -> "Unknown"
+    }
+    return "OK"
+}

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

@@ -1,6 +1,5 @@
 STEP 0:
     dependencies: stdlib, lib1, lib2
     dirty: m.kt
-
 STEP 1:
     dependencies: stdlib, lib2

js/js.translator/testData/incremental/invalidation/removeModule/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: lib2