Gtk: Initialize GTK automatically if using GTK 4

If using GTK 4, (or another future GTK version where Gtk.init() takes no
arguments) then call Gtk.init_check() automatically when importing the
library.

Use Gtk.init_check() instead of Gtk.init(), and throw an exception on
failure, so that if the programmer wants to fall back somehow to a text
interface instead of aborting the program, they can do so.
20 jobs for gtk-init in 5 minutes and 25 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Prepare
passed #1162748
build-alpine-image

00:00:33

 
  Source Check
passed #1162749
build_recommended

00:01:15

passed #1162754
codespell

00:00:27

passed #1162750
cppcheck

00:00:35

passed #1162751
cpplint

00:01:14

passed #1162752
eslint

00:01:09

passed #1162753
iwyu

00:00:29

passed #1162755
license-check

00:00:21

 
  Test
passed #1162757
build_maximal

00:01:52

passed #1162758
build_minimal

00:01:10

passed #1162767
asan
sanitizer_gcc

00:01:43

failed #1162756
asan
sanitizer_gcc

00:05:28

 
  Manual
manual #1162759
allowed to fail manual
coverage
manual #1162762
allowed to fail manual
installed_tests
manual #1162760
allowed to fail manual
iwyu-full
manual #1162761
asan allowed to fail manual
sanitizer_clang
manual #1162763
allowed to fail manual
valgrind
manual #1162766
allowed to fail manual
zeal_11
manual #1162764
allowed to fail manual
zeal_2
manual #1162765
allowed to fail manual
zeal_4