Commit `6652635` fixed autohide issues when `zwf_shell_manager_v2` isn't
available, but changed, as a side effect, the behaviour of the window's
`auto_exclusive_zone`, causing an unnecessary dependency on the
`zwf_shell_manager_v2` for the exclusive zone as well, affecting
wf-panel when the compositor's wayfire-shell plugin is disabled (see
issue WayfireWM#198 for details).

Fix it by refactoring the `WayfireAutohidingWindow` class, dividing some
methods charged with too much roles (i.e the
`WayfireAutohidingWindow::set_autoexclusive_zone()`), transfering
constructor code into new methods, introducing some new logic controls
both in the class body and in the callbacks.

Signed-off-by: Ágatha Isabelle Moreira Guedes <me@agatha.dev>

As suggested in PR WayfireWM#199 [1], this information is better retrieved by
checking whether `output->output` is not NULL.

[1] WayfireWM#199 (comment)

Signed-off-by: Ágatha Isabelle Moreira Guedes <me@agatha.dev>

As suggested [1], remove the `autohide_enable` boolean and rely on the
previously existing ones only.

[1] Comments for Pull-Request WayfireWM#199.
WayfireWM#199 (comment)

Signed-off-by: Ágatha Isabelle Moreira Guedes <me@agatha.dev>