Commit c7e597cf7278 tried to improve the slide animations when entering
the overview by using the same time as the overall overview animation,
but in fact broke the animation most of the times.
That is because the Overview imports OverviewControls before defining
the ANIMATION_TIME variable, so any javascript code that is evaluated
during that import will see the value as "undefined" (which is converted
to 0 for the animation).
Fix this by moving the ANIMATION_TIME variable before the imports instead
of the usual placement.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1331
(cherry picked from commit 26d27fdbf8477960595ae79514f9b7b8b791ae73)
a9c74ed78f