In order to more easily create global objects, we refactor code that
deals with them into gjs/global.cpp and gjs/global.h. Previously global
objects were set up partly in gjs_context_constructed() and partly in
gjs_init_context_standard(); we disentangle that code and move everything
dealing with setting up the GjsContext into gjs_context_constructed(),
while global object setup moves to gjs_create_global_object().

Since global objects all share the same root importer, we must split the
setup into two. Creating the root importer is the responsibility of
gjs_context_constructed(), and it requires that the first global has been
created. After creating the root importer, the global object is finished
with gjs_define_global_properties().

In the case of global objects beyond the first, such as the global object
for the coverage compartment, gjs_define_global_properties() will also
wrap the root importer in a cross-compartment wrapper so that the new
global can access it.

https://bugzilla.gnome.org/show_bug.cgi?id=781429