Removes the init() function in favor of executing all environment
changes when the file is imported.
Additionally ports all unit tests using imports.gi.environment.init() to
use the updated module.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2822>
While we have some style inconsistencies - mostly regarding split lines,
i.e. aligning to the first arguments vs. a four-space indent - there are
a couple of places where the spacing is simply wrong. Fix those.
Spotted by eslint.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/608
