wayland: Update sctk to 0.21, and bump MSRV to 1.86

[ids1024]

Prototyping API change in upcoming wayland-rs API release.

Smithay/client-toolkit#519

• Tested on all platforms changed
• Added an entry to the changelog module if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality

[kchibisov]

@ids1024 what's the status of this given that sctk-0.21 is released and also lays some ground for the wayland-rs change?

We may bump sctk to 0.21 for the next release of winit, I guess?

[ids1024]

Thanks for reminding me. Once PolyMeilex/sctk-adwaita#92 is released, we can update winit to use the latest sctk changes. I'll split off the change for the upcoming wayland-rs release here.

CI is failing since sctk requires Rust 1.86, while it currently targets 1.85. I assume we can just bump that since it would clearly be consistent with winit's MSRV policy.

[ids1024]

May as well merge this part into winit now.

The change to use user-data types in sctk is potentially the most error prone part of this and the wayland-rs update, since .data() has no way of checking the right type is used at compile time. I think I've updated that correctly. Otherwise the changes are fairly straightforward.