This improves the source generating process by:
* Generating the sources in the libgtk build directory, so that we do not
pollute the source tree.
* Support generating gtk[private]typebuiltins.[c|h] in the Visual Studio
projects by using NMake internally.
* Update the projects and the introspection build files so that the generated
sources and headers can be found.
This will enable us to not confuse with the deprecated headers in
gtk/deprecated as those headers are also listed under deprecated_h_sources in
gtk/deprecated/Makefile.inc, when we include the makefile snippets in both
gdk/ and gtk/.
We can regenerate demos.h.win32 with or without the font features demo
by using the regenerate-demos-h-win32 target with or without secifying
the FONT_FEATURES_DEMO=1 flag on the NMake command line.
Differently from the meson case, here we just include the emoji data
files into the global gresources file, get_emoji_data() supports this
and it's just easier to handle in these build systems.
