Add Documentation + Example Code for Getting Array Element from Function

**Your Godot version:**
v4.2.2.stable.official [15073afe3]

**Issue description:**
One example is how the documentation for dictionaries and enums show how to print all keys and their values via the .keys() function, but doesn't mention that it's possible to access a single key at a given index of .keys(). In my case I was looking for syntax to do this, which I found information on at this forum post:
https://forum.godotengine.org/t/taking-an-enum-name-instead-of-its-value/24261/3

The documentation page for Array may be a good place for this information.

**URL to the documentation page (if already existing):**

https://docs.godotengine.org/en/stable/classes/class_array.html

https://docs.godotengine.org/en/stable/classes/class_dictionary.html

https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_basics.html#enums