Render text into textures

Currently, text is rendered using the sprite sheet pipeline. This has various issues:

- Breaks code encapsulation: They are similar, but linking them makes it harder to develop features for text rendering and vice versa.
- Is really slow: (see #1122)
- Blocks #1158

I propose text rendering is done using a specialized pipeline, rendering the text into a texture that can stay on the GPU improving performance, and enabling text to use the same render pipeline the rest of the UI systems use.

As an alternative, optimization could be done elsewhere, and spritesheets and text could stay linked, but neither would allow the approach in #1158 (or a possible reimplementation).