JVM, JS: Use faster checks in IdePlatformKind.supportsTargetPlatform()

js/js.config/src/org/jetbrains/kotlin/platform/js/JsPlatform.kt

@@ -34,4 +34,6 @@ object JsPlatforms {
     val allJsPlatforms: List<TargetPlatform> = listOf(defaultJsPlatform)
 }
 
+// TODO: temporarily conservative implementation; use the same approach as for TargetPlatform?.isNative()
+//  when JsPlatform will become parameterized with "JS target"
 fun TargetPlatform?.isJs(): Boolean = this?.singleOrNull() is JsPlatform