these should only be set on commit. doing so before then confuses
code that expects these fields to be in sync with the scene tree,
such as `handle_commit`.
these were only being set so that `view_center` could read them to
compute a centered position, so instead we can simply forward the
values directly to `view_compute_centered_position` and `view_move`.
- Store a pointer to the `struct view` in `struct ssd`
- Pass `struct ssd *` instead of `struct view *` to ssd functions
- Add `ssd_get_margin()` convenience function
Gather related logic from `reload_config_and_theme()` in `server.c` and
`ssd_reload()` in `ssd.c` into a new function, `view_reload_ssd()`.
Also drop the `view->mapped` check since we want to update any view that
has SSD nodes created, mapped or not.
Add xdg_surface_from_view() + xwayland_surface_from_view() accessors
that assert() the view is of the expected type before returning.
Fix a real bug in xdg.c parent_of() that dereferenced
`view->xdg_surface->toplevel` without first checking `view->type`.
The goal of the new accessors is to catch similar bugs in future.
IMHO it encourages better design (by making dependencies more obvious)
to have source file/header file pairs like view.c/view.h, rather than a
monolithic header like labwc.h with everything in it.
I don't think we need to break up all of labwc.h at once, but maybe we
can start pulling it apart bit by bit as it's convenient.
Also:
- Move "struct border" to ssd.h so that view.h can use it without pulling
in all of labwc.h.
- Add a missing required #include within scaled_font_buffer.h (forward
declaration of "struct font" is not enough).
