Provide extension unsafeCast for dynamic.

#KT-15310

js/js.libraries/src/core/dynamic.kt

@@ -23,6 +23,13 @@ public inline fun Any?.asDynamic(): dynamic = this
  */
 public inline fun <T> Any?.unsafeCast(): @kotlin.internal.NoInfer T = this.asDynamic()
 
+/**
+ * Reinterprets this `dynamic` value as a value of the specified type [T] without any actual type checking.
+ */
+@kotlin.internal.DynamicExtension
+@JsName("unsafeCastDynamic")
+public inline fun <T> dynamic.unsafeCast(): @kotlin.internal.NoInfer T = this
+
 // TODO add the support ES6 iterators
 @kotlin.internal.DynamicExtension
 public operator fun dynamic.iterator(): Iterator<dynamic> {