wayland: Schedule a configure event when borders change

Window::checkWorkspacePosition() before the window is mapped is still
problematic and should be avoided as it can produce undesired constrained
client size (1x1).

Given that XdgToplevelWindow tries to maintain the same frame geometry
size, it should be enough to schedule another configure event instead.
It is going to be in line with the other decoration logic in the
XdgToplevelWindow and it's a better way to handle async geometry updates.

BUG: 480910
(cherry picked from commit e974c070)