Some (mostly) regression fixes for the Objects dialog

Commit 1: Fix broken Layer specific actions

Post GTK4 migration, InkscapeWindow::activate_action needs "win." prefix to work. Unbreaks delete, move up/ move down buttons in Layers only mode

Commit 2: Fix layers dialog moving 1px on hover

This is really a regression in the way css applies to GtkTreeView in Gtk4 (it applies to the entire view and not just the rows), but I don't think that would get fixed since treeviews have been deprecated. I've attempted to maintain some kind of hover effect, but it really feels like a hack. Perhaps there's a better way of doing it? I guess the ideal fix would be to port away from treeview.

Comparison

Before	After

Commit 3: Defer 'selection' of layer back to the second click

Fixes inbox#11687 (closed) - I tested all issues fixed by 9360f8a3 and none of them seem to require this, so maybe it is not necessary? (@VaibhavMalik4187 can you confirm?)

Commit 4: Fix tag color rendering and setting