Those property features don't seem to be in use anywhere.
They are redundant since the docs cover the same information
and more. They also created unnecessary translation work.

Closes #4904

Add some more docs around GtkIMContext.

Replace leftover gtk-doc syntax (#Type) with backquotes.

allow-none has been deprecated for a long time
already. Instead use optional and nullable everywhere.

Mostly fixing up indentation of continuation lines,
and other small cleanups.

The Wayland text protocol expects to get both ends
of the selection with its surrounding call, so make
that available via GtkIMContext. We add this as new
api and vfuncs, and fall back, so that existing
implementations keep working.

Replace most remaining uses of GTK+ in the docs and
user-visible strings by GTK. Also remove some leftover
"Was added in 3.x" sentences from the docs.

Query the seat for that.

Make GdkEvents hold a single GdkDevice. This device is closer to
the logical device conceptually, although it must be sufficient for
device checks (i.e. GdkInputSource), which makes it similar to the
physical devices.

Make the logical devices have a more accurate GdkInputSource where
needed, and conflate the event devices altogether.

We already use the "logical/virtual" and "physical" names in the
documentation, there's no reason to use loaded terms just because X11
uses them.

An event-less variant of the filtering api.

We should just use GdkEvent, instead of taking
a GdkEventKey, and then cast it everywhere.

We don't need to cover every case with a va_marshaller, but there are a
number of them that are useful because they will often only be connected
to by a single signal handler.

Generally speaking, if I opened into a file to add a va_marshaller, I just
set all of them.

There is now a set_client_widget() to hint the IM about positioning
and whatnot.

glib will use the correct marshaller automatically. And as a side
effect, we also get all glib optimizations, like a va marshaller.

Instead of Return value:

https://wiki.gnome.org/Design/OS/Typography

https://bugzilla.gnome.org/show_bug.cgi?id=723119

https://bugzilla.gnome.org/show_bug.cgi?id=723119

https://bugzilla.gnome.org/show_bug.cgi?id=702996

They are no longer used.

Add input-purpose and input-hints properties to GtkIMContext.

https://bugzilla.gnome.org/show_bug.cgi?id=651244

The introspection annotation for gtk_im_context_get_surrounding
was missing a :.

- add gtkmodulesprivate.h and move stuff there from gtkprivate.h
- add gtkprivate.c and move stuff there from gtkmain.c
- add gtkwin32.c and move stuff there from gtkmain.c
- don't redefine GTK_DATADIR and friends in gtkprivate.h
- have _gtk_get_datadir() and friends on all platforms
- remove the horrid hacks where gtkprivate.h can't be included,
  or must be included later due to redefinition of the compile-time
  directories