Screen geometry changed events could end up connected to the wrong
views, or not at all. This could cause greeters not to be visible (and
as such desktop contents visible), greeters at the wrong size or
position and/or overlapped.

We map Qt screens() by index to our own list of m_views, but Qt is free
to reorder screens, and when screens are removed, what used to be e.g.
index 0 could be removed, leading to connect() pointer to pointer
mappings being incorrect. Since we also set geometry on add/remove this
can lead to us changing to the correct geometry then back to geometry
that is not covered by active screen, essentially making the greeter
invisible, and no valid greeter visible.

Since there is no uniqueness constraint for lambda connections, we can
also end up with multiple screens updating different geometries on the
same view, or repeated signals from the same screen.

Fix this by only connecting screens once, and having the receiving
lambda resolve the index to index mapping so connections are persistant
with the life of the screen.

BUG: 347934