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>
The markup unit test currently fails with the following message:
TypeError: class heritage MessageList.Message is not an object or null
This is because MessageList imports other modules that end up importing
MessageList themselves in order to inherit from one of its classes. But
as the MessageList imports hasn't finished yet (it's still processing
its own imports), that class hasn't been defined yet.
Work around that by importing Main first, so that the importer can
process imports in a proper order.
js2-mode is no longer developed and we recommend js-mode these days,
so switch the modelines to specify that, and make them consistent
across all files.
https://bugzilla.gnome.org/show_bug.cgi?id=660358
