Use separate system properties to control IC for JVM and JS

Also this commit effectively disables JS IC by default

     #KT-25563 fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/MultifileClassCodegen.kt

@@ -383,7 +383,7 @@ class MultifileClassCodegenImpl(
         private fun getCompiledPackageFragment(
                 facadeFqName: FqName, state: GenerationState
         ): IncrementalPackageFragmentProvider.IncrementalMultifileClassPackageFragment? {
-            if (!IncrementalCompilation.isEnabled()) return null
+            if (!IncrementalCompilation.isEnabledForJvm()) return null
 
             val packageFqName = facadeFqName.parent()