glib_typeof: Move definition to its own header

It is cleaner to define glib_typeof() in a header included after
gversionmacros.h so we can use GLIB_VERSION_MIN_REQUIRED directly
instead of doing it everywhere glib_typeof() is used.
10 jobs for gtypeof in 22 minutes and 28 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Style Check
passed check-todos #1307980

00:00:38

failed style-check-diff #1307979
allowed to fail

00:00:38

 
  Build
passed cross-android_api21_arm64 #1307983

00:00:38

passed cross-android_api28_arm64 #1307984

00:01:59

passed cross-mingw64 #1307985

00:00:52

passed debian-stable-x86_64 #1307982

00:02:41

passed fedora-x86_64 #1307981

00:04:44

passed msys2-mingw32 #1307986
win32-ps

00:15:45

passed vs2017-x64 #1307987
win32-ps

00:08:12

 
  Coverage
passed coverage #1307988

00:01:57

76.1%
 
Name Stage Failure
failed
style-check-diff Style Check
 
+#include <glib/glib-typeof.h>
#include <glib/gmem.h>
-#include <glib/glib-typeof.h>

G_BEGIN_DECLS

Cleaning up file based variables
ERROR: Job failed: exit code 1