Add back fullname property at scan matching phase

There seems to be a lot of config files using fullname property in the world.
To keep the backward compatibility, fullname property is back to a cache at
the scan matching phase but will be rebuilt once it is done according to family
and style property in the pattern no matter what changes one made in fullname
property during that.

Ref. https://bugzilla.redhat.com/show_bug.cgi?id=1902881
10 jobs for fixup-fullname-prop in 7 minutes and 49 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed meson macos #5967355
gst-macos-10.15

00:02:37

passed meson-mingw-w64-build #5967352

00:06:42

manual meson msys2 #5967356
docker windows 1809 allowed to fail manual
passed meson-shared-build #5967350

00:06:24

passed meson-static-build #5967351

00:06:28

passed meson vs2017 amd64 #5967353
docker windows 1809

00:01:25

passed meson vs2017 x86 #5967354
docker windows 1809

00:01:24

passed mingw-build #5967349

00:06:37

passed shared-build #5967347

00:07:48

passed static-build #5967348

00:06:31