Merge troika-3d-text package into troika-3d

[lojjic]

The troika-3d-text package has had an interesting evolution.

• It originally contained everything related to text rendering, coupled tightly with the troika-3d framework package.
• When it became obvious it was useful/needed in the larger Three.js community, it was given a custom standalone build file that decoupled the Three.js code from the troika-3d framework code.
• Then for better ergonomics all the standalone code was extracted to the new generic troika-three-text package.
• That left just Text3DFacade and the partially-completed helpers for text selection.
• Now work is underway to move the text selection logic into troika-three-text too, so it will be just the Text3DFacade remaining.

It doesn't really make sense to have a separate package for just that. So I'd like to move Text3DFacade into troika-3d and retire the troika-3d-text package. Bloating the troika-3d package size isn't an issue I don't think, and it should be treeshakeable if unused.