The environment module is used to initialize the environment, yet it
currently also defines the adjustAnimationTime() function.
Ideally it should not export any utility functions, in particular
once converted to ESM.
The function cannot be moved to the existing Utils module, as that
depends on an initialized environment, and can therefore not be
imported from environment.js, so use that opportunity to group
together several animation helpers in a new animationUtils module.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2822>
