[JS IR] IC improvements

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

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

@@ -8,4 +8,7 @@ class BoxConsumer: Consumer<String> {
 
 fun test(producer: Producer<String>, consumer: Consumer<String>) = consumer.consume(producer.produce())
 
-fun box() = test(BoxProducer(), BoxConsumer())
+fun box(): String {
+    if (test(BoxProducer(), BoxConsumer()) != 4) return "Fail"
+    return "OK"
+}

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

@@ -1,7 +1,5 @@
 STEP 0:
     dependencies: stdlib, lib1
     dirty: m.kt
-STEP 1:
-    dependencies: stdlib, lib1
-STEP 2:
+STEP 1..2:
     dependencies: stdlib, lib1