gdk: x11: Fill GdkMonitor manufacturer with PNP id from EDID

Previously, the manufacturer property of the GdkMonitor was NULL,
and having at least PNP id at GdkMonitor.manufacturer makes it
possible to distinguish between different monitors programmatically.
4 jobs for gdkmonitor-x11-manufacturer-stable in 25 minutes and 59 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #337025
fedora-autotools

00:25:59

passed #337026
fedora-meson

00:07:22

manual #337028
win32 allowed to fail manual
msys2-mingw32-autotools
passed #337027
win32
msys2-mingw32-meson

00:21:21