[wgpu-hal] Upgrade to `glutin` 0.31.3, narrow `libloading` to 0.8

[ErichDonGubler]

This eliminates a ton of duplicate dependencies. Woot! Firefox is finally ready for incremental update of libloading, so we can make this change without any hassle. 😀

~~Depends on #5504, to have no dependency on libloading 0.7.~~

[cwfitzgerald]

This can be un-drafted

[ErichDonGubler]

@cwfitzgerald: It seems we need to pick an optional backend feature for glutin now (as indicated by CI)? I don't know immediately what the right answer is, tho. 😖

[teoxoy]

They get automatically enabled, the issue is that iOS support was removed in v0.30.

So, I think we should just skip building the example on iOS.

[teoxoy]

What about this? Should we remove it or bump it as well?

https://github.com/gfx-rs/wgpu/blob/77a83fb0dd9f2295f25e99a850b9a031738925c3/Cargo.toml#L154

[MarijnS95]

@ErichDonGubler what's needed to finish this, port the raw-gles.rs example because glutin completely removed winit from its core and is now a proper wrapper around GL context creation (kind of doing the exact same thing as your wgl.rs, egl.rs etc)?

I'd love to push this through to further reduce dependencies on winapi :)

[ErichDonGubler]

@MarijnS95: Honestly, this just needs somebody to drive it to completion. I'm happy to cede this PR to you, if you have the bandwidth.

[MarijnS95]

@ErichDonGubler bandwidth is tight, but I've written and worked on my fair share of glutin codebases over the years so I might be able to pick this up and get it over with in a short amount of time.

[Wumpf]

https://github.com/gfx-rs/wgpu/pull/5709 highlights that glutin drags in winit right now, making it a holdout for winit 0.27 (dev dependency only still though)