Core: Add Callable.create static method for Variant callables

modules/gdscript/tests/scripts/runtime/features/builtin_method_as_callable.gd

@@ -1,6 +1,13 @@
 func test():
 	var array: Array = [1, 2, 3]
 	print(array)
-	var callable: Callable = array.clear
-	callable.call()
+	var array_clear: Callable = array.clear
+	array_clear.call()
 	print(array)
+
+	var dictionary: Dictionary = {1: 2, 3: 4}
+	print(dictionary)
+	# `dictionary.clear` is treated as a key.
+	var dictionary_clear := Callable.create(dictionary, &"clear")
+	dictionary_clear.call()
+	print(dictionary)

modules/gdscript/tests/scripts/runtime/features/builtin_method_as_callable.out

@@ -1,3 +1,5 @@
 GDTEST_OK
 [1, 2, 3]
 []
+{ 1: 2, 3: 4 }
+{  }