IBusInputContext/ClutterInputFocus/GtkIMContext all go for offset+len
for their ::delete-surrounding signals, with offset being a signed int
(neg. to delete towards left of selection, pos. to delete towards right
of selection) and len being an unsigned int from the offset (and
presumably, skipping the current selection).
The text-input protocols however pass in this event two unsigned integers,
one being the length of text to delete towards the left of the selection,
and another the length of text to delete towards the right of the selection.
To translate properly these semantics, positive offsets shouldn't account
for before_length, and negative offset+len shouldn't account for after_length.
The offset/length approach may of course represent deletions that are
detached from the current cursor/selection, we simply delete the whole range
from the cursor/selection positions then.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/517
The input method can assign a negative value to
clutter_input_method_delete_surrounding() to move the cursor to the left.
But Wayland protocol accepts positive values in delete_surrounding() and
GTK converts the values to the negative ones in
text_input_delete_surrounding_text_apply().
https://gitlab.gnome.org/GNOME/mutter/issues/539
The order and way include macros were structured was chaotic, with no
real common thread between files. Try to tidy up the mess with some
common scheme, to make things look less messy.
