Summary:
Commit 5d9027b1 introduced a regression in TabBox by using the generic
framework inside KWin to test for same application. What I did not
consider was that the code in TabBox was "broken by design". It didn't
use the generic check as that is too strict and considers windows from
different processes as not belonging to the same application. But this
is not wanted in the case of TabBox.

On the other hand the change itself is an improvement to also support
Wayland in a better way and not have special handling situations. Thus
just reverting would not help.

Instead this change addresses the problem by extending the internal API
and to allow more adjustements. So far there was already an
"active_hack" boolean flag. This is extended to proper flags with an
additional flag to allow cross application checks.

The checks in Client which would filter out different applications check
for this flag and are skipped if set. In addition ShellClient also adds...