This changes the state handling logic of wl_surface to automatically
track subsurface pending in the form of transactions. The role enum
(and the associated type parameter) is no more, and replaced by a
general-purpose typemap-like container on surfaces.
The new logic is introduced in the files:
- `src/wayland/compositor/cache.rs`
- `src/wayland/compositor/transaction.rs`
The rest of the PR is the fallout of these changes, as well as a few
trivial clippy fixes.
Victor Berger