commands: Add per-view shortcuts_inhibitor command

Add a separate per-view shortcuts_inhibitor command that can be used
with criteria to override the per-seat defaults. This allows to e.g.
disable shortcuts inhibiting globally but enable it for specific,
known-good virtualization and remote desktop software or, alternatively,
to blacklist that one slightly broken piece of software that just
doesn't seem to get it right but insists on trying.

Add a flag to sway_view and handling logic in the input manager that
respects that flag if configured but falls back to per-seat config
otherwise. Add the actual command but with just enable and disable
subcommands since there's no value in duplicating the per-seat
activate/deactivate/toggle logic here. Split the inhibitor retrieval
helper in two so we can use the backend half in the command to retrieve
inhibitors for a specific surface and not just the currently focused
one. Extend the manual page with documentation of the command and
references to its per-seat sibling and usefulness with criteria.

Signed-off-by: Michael Weiser <michael.weiser@gmx.de>

sway/tree/view.c

@@ -36,6 +36,7 @@ void view_init(struct sway_view *view, enum sway_view_type type,
 	view->impl = impl;
 	view->executed_criteria = create_list();
 	view->allow_request_urgent = true;
+	view->shortcuts_inhibit = SHORTCUTS_INHIBIT_DEFAULT;
 	wl_signal_init(&view->events.unmap);
 }