This adds a `unstable-wgpu-24` feature that exposes WGPU types in the
GraphicsAPI enum, adds `require_wgpu_24()` to the backend selector,
and adds a conversion from `wgpu::Texture` to `slint::Image`.
The `require_wgpu_24()` function in the selector will be extended in the
future (before the next release) to permit specifying additional aspects
of the WGPU configuration.
Co-Authored-By: Olivier Goffart <olivier.goffart@slint.dev>
