Rename KClass<*>.isInterface helper in the JS part (#3027)

We are going to introduce a new KClass member in
the standard library with the same name marked
with an opt-in annotation, so in the usages of this
extension property would stop compiling because
the member is always favored and there is no opt-in.

See KT-78581

Author: broadwaylamb

core/jsMain/src/kotlinx/serialization/internal/Platform.kt

@@ -26,7 +26,7 @@ internal actual fun <T : Any> KClass<T>.compiledSerializerImpl(): KSerializer<T>
         else this.js.asDynamic().Companion?.serializer()
         ) as? KSerializer<T>
 
-internal actual fun <T: Any> KClass<T>.isInterface(): Boolean = isInterface
+internal actual fun <T: Any> KClass<T>.isInterface(): Boolean = isInterfaceHack
 
 internal actual fun <T> createCache(factory: (KClass<*>) -> KSerializer<T>?): SerializerCache<T> {
     return object: SerializerCache<T> {
@@ -73,8 +73,10 @@ internal actual fun isReferenceArray(rootClass: KClass<Any>): Boolean = rootClas
  * WARNING: may be broken in arbitrary time in the future without notice
  *
  * Should be eventually replaced with compiler intrinsics
+ *
+ * TODO: Remove this when KT-78581 lands into a 2.2.20 release
  */
-private val KClass<*>.isInterface: Boolean
+private val KClass<*>.isInterfaceHack: Boolean
     get(): Boolean {
         // .js throws an exception for Nothing
         if (this === Nothing::class) return false