Port to GTK4

[tfuxu]

This is a port of TextSnatcher to GTK4 and Granite 7. It's almost done, but there are still some things that I need to finish, like ~popover menu for languages~ (done), and a Copy from Clipboard option.

Current appearance in GNOME (updated):

TextSnatcher on GTK3 in GNOME for a contrast:

PS. Sorry for a messy code, I started learning Vala about 1 week ago :^)

[RajSolai]

Wow great !, I was thinking of port to GTK4 from today, Thanks for your contribution @tfuxu will be merging to a new branch for gtk4

[tfuxu]

@RajSolai Just as a note: if you are going to fix Copy from Clipboard option yourself, in GTK4 you should use read_texture_async function. You should also check a clipboard section in 3-to-4 guide here: https://docs.gtk.org/gtk4/migrating-3to4.html#replace-gtkclipboard-with-gdkclipboard