Give a hint on how to remove array's element while iterating over it

**Your Godot version:**
Godot 4.6

**Issue description:**
Class: Array

I was searching how to iterate through an array to remove/erase some of its elements. When I first read the docs, I understood that erasing while iterating on an array is not possible at all. The first comment of this [reddit post](https://www.reddit.com/r/godot/comments/z7b2kb/i_always_forgot_how_a_for_loop_manipulating_an/) advises to loop backward and to use `remove_at`. I think it would be nice to indicate in the docs that is possible to remove element this way, eventually directly providing a code snippet.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/4.6/classes/class_array.html#class-array-method-erase

Start at the Godot 4.6 Array documentation's erase section and review the existing guidance around remove_at. Add a clear hint or code snippet showing backward iteration for removing elements, then verify that the documentation explains when this approach is appropriate.

Written by the indexing model from the issue text.