Proposal: move wgpu.gui into a new library

[almarklein]

TL;DR

• We're moving wgpu.gui into a new library called rendercanvas: https://github.com/pygfx/rendercanvas
• The wgpu.gui will remain working for a while, to ease transition.
  • This means updates to wgpu can be applied, and new releases be made, without interfering with this transition.
• We'll create documentation on how to update to rendercanvas.
• When we get to the "update propagation" work in Pygfx, Pygfx will switch to rendercanvas.
• The wgpu.gui will be deprecated sometime after the "update propagation" changes in pygfx are all done. Nu rush.

---

In earlier work the API for the canvas was separated better from wgpu itself. The idea was that in principal it should be considered a separate package. I now think we should really make it a separate package.

In short, the reason is that the canvas logic and API are about orthogonal to wgpu. It also solves a completely different problem. Things like tests and docs are also very different. Also, wgpu can be used without a canvas, and a canvas can potentially also be used without wgpu (it already supports displaying bitmap images).

With the rework that's on the way in #618 (and follow-up prs), I think now would be a really good time. We can apply all the new stuff (which will change the API a bit) to the new library, while we keep wgpu.gui as-is until we gradually deprecate it.

The purpose of the new lib would be the same as our current wgpu.gui, but let's make it explicit:

• Providing a generic canvas API to render to (with wgpu).
• Providing canvas implementations for various GUI libraries (e.g. qt and wx) and platform (e.g. Jupyter, browser).
• Providing an event system with standardized event objects.
• Providing an event loop and scheduling.

[almarklein]

https://github.com/pygfx/rendercanvas

[almarklein]

My proposal is:

from rendercanvas.auto import RenderCanvas

That name is free and pretty clear: it's a canvas to render to. Not wgpu-specific, actually, since anything that can render using either a window-id, or by providing an image, can use it.

If you feel like bike-shedding on the name, I'm up for it 😄

---

I want to use the same select-by-import mechanics as before, and extend it a little bit:

# Auto-select
from rendercanvas.auto import RenderCanvas

# Explicit lib
from rendercanvas.glfw import RenderCanvas

# Qt needs to know what lib to use
import PySide6
from rendercanvas.qt import RenderCanvas

# Let's also make this work
from rendercanvas.pyside6 import RenderCanvas 

# If you have a renderer that only produces images
from rendercanvas.auto_image import RenderCanvas

[almarklein]

I added a quick summary in the top post to what this change means for downstream libraries. In short: no rush yet.

[almarklein]

I moved multiple issues, that related to the canvas, from wgpupy to the rendercanvas repo.