Refactor ColorPicker shapes

[KoBeWi]

Closes godotengine/godot-proposals#4353
Basically #62075, but for picker shapes.

Adds a new class ColorPickerShape, which is an abstraction of picker shapes (similar to ColorMode). This allows to split some behemoth methods into a more manageable pieces. For now I removed the huge _hsv_draw() method, which had entangled code for drawing every piece of ColorPicker. Now each part has its own method. The shapes should appear as before.

[KoBeWi]

I reimplemented the input. The shapes should behave the same as before.
Feel free to test, I'm not sure if deferred mode is done correctly.

I'll be probably changing the shapes to be Object, because the current code is far from ideal and the little saved memory is not worth it.

[KoBeWi]

Rebased. There were many changes to ColorPicker in the meantime, hopefully I didn't accidentally revert anything.

[Calinou]

Tested locally (in the editor and a minimal project), it mostly works as expected.

I spotted one functional regression though. ColorPickerButton with the OKHSL slider mode (not the color wheel mode) will have the color wheel disappear entirely, while a standalone ColorPicker with the same setting is fine.

Before	After

[KoBeWi]

Good catch, fixed.

[Calinou]

Works great now 🙂

Code looks good to me.

[akien-mga]

Thanks!