Godot: AnimatedTexture sprite sheet support

[TheDuriel]

Godot version:

3.1

Issue description:

AnimatedTexture is not capable of using AtlasTextures for its frames. When loading an AtlasTexture the animation will stop, and the entire first frame displays.

Steps to reproduce:
Create an AnimatedTexture with four frames. Make each frame an AtlasTexture that is one quarter of the Godot Icon.

Comment:

We should document which texture types animated texture supports.
I would also like the ability for AnimatedTexture to support sprite sheets, this would make it much easier to configure them in general. And makes it more convenient to use them as shader flipbooks. For effects such as described in this GDC talk: https://www.gdcvault.com/play/1024630/Visual-Effects-Bootcamp-The-Rise (Technically you can do it without sprite sheets. but its quite a hassle because the workflow is dreadfully slow.)

[nobuyukinyuu]

support for AtlasTextures seems like it would be a minimum requirement for animating such things as TileMaps, seeing as how most people don't store tilesets any other way except densely-packed...

[Byteron]

there are the issues #30295 and #32653 about the issues with using AtlasTextures in AnimatedTextures.

[akien-mga]

See also example project from #32653:

Steps to reproduce:
https://imgur.com/a/76RF7hB
Minimal reproduction project:
https://github.com/MasterGordon/animatedtexturetest

[Shadowblitz16]

just ran into this issue and now that I see this idk how to work around it
EDIT: how is this not labeled as a bug?
animated texture takes a array of textures which should support a atlas texture