cogl-pango is conceptually a separate library so it doesn't seem
appropriate to bundle the headers with all the other cogl headers. Also
in-tree the headers live in a cogl-pango directory so if we want
examples that can include cogl-pango consistently when built in or out
of tree using the convention #include <cogl-pango/cogl-pango.h> makes
that easy.
This adds a compatibility cogl/cogl-pango.h header that's will redirect
to cogl-pango/cogl-pango.h with a warning, or result in an error if
COGL_ENABLE_EXPERIMENTAL_2_0_API is defined.
Some of the sources need to include <cogl/cogl-defines.h> which is in
the build directory. I think this directory gets added to the include
flags anyway by something so the actual building works but when
building the introspection data out of tree it was not included so it
failed to scan.
This removes all the remnants from being able to build Cogl standalone
while it was part of the Clutter repository. Now that Cogl has been
split out then standalone builds are the only option.
