gtk: Use our own g_log callbacks
Only for gtk4- and gtk3.22-clients also in S3_1 - not for gtk3-client, as there's dependency on relatively new glib version (if we really wanted this for gtk3-client, we could port it with reduced functionality, but doesn't seem worth it)
We should insert our own g_log callbacks, 1) to get the logs within our own freelog, 2) to have a place for a breakpoint, and 3) to get fcbacktrace produced in error situations.
I've got something to work on gtk3.22-client. Lot of work needed to clean it up even for that client, and may need changes to gtk4-client (thought this is glib, not gtk functionality)