Two fixes for text field accessibility:
1. Fix character count being off by one due to trailing newline always
being appended to the last line. Add `is_last_line` parameter to
`accessibility_create_sub_text_edit_elements()` to control this.
2. Link adjacent TextRuns via `previous_on_line`/`next_on_line` so
screen readers can properly navigate lines. Without these links,
AccessKit treats each TextRun as a separate line, causing incorrect
announcements when arrowing through multi-line text.
The backend is now mature enough to not explode with multiple windows
but the `DisplayServer` API still cannot meet some guarantees required
by the various Wayland protocols we use. To meet those guarantees this
patch adds three new elements to the DisplayServer API, with relative
handling logic for `Window` and `Popup` nodes:
- `WINDOW_EVENT_FORCE_CLOSE`, which tells a window to *forcefully*
close itself and ensure a proper cleanup of its references, as Wayland
enforces this behavior;
- `WINDOW_FLAG_POPUP_WM_HINT`, which explicitly declares a window as a
"popup", as Wayland enforces this distinction and heuristics are not
reliable enough;
- `FEATURE_SELF_FITTING_WINDOWS`, which signals that the compositor can
fit windows to the screen automatically and that nodes should not do
that themselves.
Given the size of this feature, this patch also includes various
`WaylandThread` reworks and fixes including:
- Improvements to frame wait logic, with fixes to various stalls and a
configurable (through a `#define`) timeout amount;
- A proper implementation of `window_can_draw`;
- Complete overhaul of pointer and tablet handling. Now everything is
always accumulated and handled only on each respective `frame` event.
This makes their logic simpler and more robust.
- Better handling of pointer leaving and pointer enter/exit event
sending;
- Keyboard focus tracking;
- More solid window references using IDs instead of raw pointers as
windows can be deleted at any time;
- More aggressive messaging to window nodes to enforce rects imposed by
the compositor.
Add a note to clarify that the DisplayServer.get_display_safe_area() method is currently only implemented on Android and iOS, and that it returns screen_get_usable_rect(SCREEN_OF_MAIN_WINDOW) as a fallback on other platforms.