[wayland] Use pending maximize mode in decoration updates

Summary:
The change to make maximize mode asynchronous featured the comment

Things are a bit complex with borders. Technically we
shouldn't update them till we get a response, but we also need to have
the correct geometry of the full size window in our request. For now
they behave as before, updating when we request the change.

We call setNoBorder when we request the geometry but decoratedClient
also checks the maximise mode, in order to follow the scheme above we
need this to operate on the requested state not current state.

X is unaffected.

This fixes the borders being restored correct after maximize/restore.

Test Plan:
Chose a theme with visible borders
Maximised a window and back
They restored

Reviewers: KWin, zzag

Reviewed By: KWin, zzag

Subscribers: zzag, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D15991