protocol: fix clarification of input region on drags and pointers
protocol: fix clarification of input region on drags and pointers

The previous clarification did not follow the current implementation in
Weston, where when a surface stops being a cursor or an icon, it becomes
a plain unmapped surface again.

Rewrite the related paragraphs, and fix some typos while at it.

For start drag, make it explicit of which surface argument we are
talking about.

v2:

Make the input region undefined when the use ends. Most likely no-one
will re-use these surfaces for anything else than the same use case, so
leave some slack for the implementations to avoid useless work on
resetting the regions.

Reported-by: Ander Conselvan de Oliveira <17227041d62225a8b18be8c9e33f1bc99023cd25@gmail.com>
Signed-off-by: Pekka Paalanen <6c0263d81461c956d504307112a4ce25eaacc3d1@gmail.com>

mchalupa/wayland,tulcod/wayland,tulcod/wayland,eyolfson/wayland,mchalupa/wayland,eyolfson/wayland,tulcod/wayland,bitfactor/wayland,sir-murray/wayland,bitfactor/wayland,abooij/wayland,eyolfson/wayland,abooij/wayland,sir-murray/wayland,sir-murray/wayland,abooij/wayland,bitfactor/wayland,mchalupa/wayland