support Gtk4

[friday]

Description

A lot of APIs we depend on were removed in Gtk4

It is too early to even start investigating all that we would need to migrate. But these should be done before:

Preparations:

• Replace wnck (depends on Gtk3) refactor: replace wnck with ewmh #1363
• Refactor to remove multiple inheritance for AppIndicator and LayerShellOverlay (Gtk4 doesn't support multiple inheritance)
• Rewrite get_monitor (method to get the active monitor) our last remaining use of GdkX11
• Replace set_keep_above with EWMH _NET_WM_ACTION_ABOVE / _NET_WM_STATE_ABOVE
• Rewrite the code to (center) position and move the window
• Replace webkit2gtk (depends on Gtk3) Rewrite Ulauncher preferences to use pure GTK (not webkit) #1257

Migration:

• Bump gi_versions for Gtk, Gdk to 4.0
• Replace Gtk.IconTheme.get_default() w Gtk.IconTheme.get_for_display(display)?
• Use new API for storing to clipboard (display.get_primary_clipboard().set_content(Gdk.ContentProvider.new_for_value(data))?)

I tried to rewrite the get_monitor method so that it used python-xlib. I managed to get the mouse coordinates:

from Xlib.display import Display
data = Display().screen().root.query_pointer()
# data.root_x and data.root_y 

However:

1. I haven't found a replacement for display.get_monitor_at_point(x, y). It's possible that we can use data.child (window) to get the actual "Window" (or virtual window if there is no window under your pointer?) but that doesn't help. We need to calculate this: https://www.reddit.com/r/commandline/comments/nko6rw/how_can_i_get_the_current_monitor_on_which_a/ (this is also what get_monitor_at_point does in the source code).
2. The coordinates we get differ from the coordinates we get from Gtk. The Gtk ones includes the scaling factor (so if your scaling factor is 2x, then the Gtk ones will be half of the Xlib ones. This might not be a problem though (since the replacement for we write for get_monitor_at_point likely won't either).

Communication guidelines

• I have read and agree with Ulauncher's communication guidelines and checked the existing enhancement requests before suggesting this.

Ulauncher v6

• I have checked and couldn't find my suggestion in v6.