[JS IR] IC improvements

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

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

@@ -1,6 +1,5 @@
 STEP 0:
     dependencies: stdlib, lib1
     dirty: l2.kt
-
 STEP 1:
     dependencies: stdlib, lib1

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

@@ -1,2 +1,15 @@
 
-fun box() = qux() == bar()
+fun box(stepId: Int): String {
+    when (stepId) {
+        0 -> {
+            if (qux() != "FOO") return "Fail qux"
+            if (bar() != "FOO") return "Fail bar"
+        }
+        1 -> {
+            if (qux() != "BAR") return "Fail qux"
+            if (bar() != "BAR") return "Fail bar"
+        }
+        else -> return "Unknown"
+    }
+    return "OK"
+}

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

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

js/js.translator/testData/incremental/invalidation/constVals/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