Allow hooking text rendering

[LPGhatguy]

It would be great to let users replace yakui's text rendering. I think a clever way that we could do this is by moving yakui's text code into a new crate, like yakui-text, and then let people use Cargo to patch-replace it.

[msparkles]

As per #179, we've figured that textboxes and text widgets are extremely dependent on the text backend! Ideally you'd just replace the widgets entirely yourself

We sure should move it to a separate crate, though, that should be the way to go in the future

[msparkles]

Perhaps not to patch it but just have a separate crate that has text widgets? During the cosmic_text PR we barely had to touch the wgpu side of things, yakui's rendering frontend is apparently enough for all that texts need?