The animation handling is kinda split between layout (for the
keyboard slide), and keyboard (for the focus window slide). It
would be nice to have more fine grained control on those, so
move the animation handling altogether to keyboard.js as a start.
This is roughly similar, except that transformations apply to
the Keyboard actor, instead of the keyboardBox (its parent). We
now queue a relayout after the animation in order to update the
chrome tracking.
The only layering break now is that we emit
layoutManager::keyboard-visible-changed in keyboard.js, its
purpose will be dropped in future commits, so leave it there for
now.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1668>
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