[JS IR] IC improvements

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

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

@@ -1,2 +1,11 @@
 
-fun box() = foo()
+fun box(stepId: Int): String {
+    when (stepId) {
+        0 -> if (foo() != 42) return "Fail"
+        1 -> if (foo() != 43) return "Fail"
+        2 -> if (foo() != "44") return "Fail"
+        3 -> if (foo() != "hello") return "Fail"
+        else -> return "Unknown"
+    }
+    return "OK"
+}

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

@@ -1,13 +1,3 @@
-STEP 0:
+STEP 0..3:
     dependencies: stdlib, lib1
     dirty: m.kt
-STEP 1:
-    dependencies: stdlib, lib1
-    dirty: m.kt
-STEP 2:
-    dependencies: stdlib, lib1
-    dirty: m.kt
-STEP 3:
-    dependencies: stdlib, lib1
-    dirty: m.kt
-