* Move GTK compatibility macros into a separate header
* Fix Cairo compatibility checks
* Move Glib-namespaced definitions to GtkCompat header
* Remove unused stringify definitions since we're using fmtlib
* Automatically (re)order include directives (GTK client)
Include our headers first to ease IWYU enforcement.
* Fix includes missing from headers (GTK client)
* Fix build on Mac after includes reordering