Remove `WebWindowHandle`?

[madsmtm]

We now have WebCanvasWindowHandle and WebOffscreenCanvasWindowHandle, which are much safer, so we should probably work on removing WebWindowHandle.

Probably with a deprecation period first.

[daxpedda]

I'm in favor of this as well.

I've implemented support for the other handles in some known crates with success so far:

• On Web, use the new WebCanvasWindowHandle winit#3270
• Web: add support for more RawWindowHandle variants gfx-rs/wgpu#4888
• Web: add support for more RawWindowHandle variants softbuffer#188

[notgull]

I think we should wait to remove these handles until we have a stable (post-1.0) way to refer to web handles, whether it's wasm-bindgen or the new wit-bindgen thing that's coming out.