Add class icons to script list, separate doc list

[aXu-AP]

Implements godotengine/godot-proposals#3557 (as per further suggestions in the thread comment)
Alternate to #96865

It's not perfect, but can be used to get feel how this suggestion works.

[Maran23]

This is a nice idea! Lets see what other people think, but I like it! :)

[Mickeon]

The only "gripe" with this is that the documentation pages can no longer be shuffled around in the list. Gonna be honest, though I don't see why you'd mix-and-match around, given that the pages appearing at the bottom is much more appealing, and they are ordered to the bottom by default anyhow.

[Mickeon]

Also, by all means, see also this comment I don't forget on a related discussion.

[aXu-AP]

Also, by all means, see also this comment I don't forget on a related discussion.

Heh, it seems to be the very same @seppoday who suggested this scripts/docs separation as well 😁
For collapsable structure, moving to Tree would give flexibility needed. In that case split wouldn't be needed to be hard coded either (altough problem of differentiating docs from scripts would return without splitting).