Clean warnings and refactor stdlib tests.

Merge RangeJVMTest into RangeTest.

libraries/stdlib/test/js/MapJsTest.kt

@@ -11,6 +11,7 @@ class ComplexMapJsTest : MapJsTest() {
         HashMap<K, Int>()
         HashMap<K, Int>(3)
         HashMap<K, Int>(3, 0.5f)
+        @Suppress("UNCHECKED_CAST")
         val map = HashMap<K, Int>(createTestMap() as HashMap<K, Int>)
 
         assertEquals(KEYS.toNormalizedList(), map.keys.toNormalizedList() as List<Any>)

libraries/stdlib/test/js/SetJsTest.kt

@@ -12,6 +12,7 @@ class ComplexSetJsTest : SetJsTest() {
         HashSet<T>(3)
         HashSet<T>(3, 0.5f)
 
+        @Suppress("UNCHECKED_CAST")
         val set = HashSet<T>(data as HashSet<T>)
 
         assertEquals(data, set)