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 11 minutes and 57 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #301899
fedora-autotools

00:10:23

passed #301900
fedora-meson

00:11:57

manual #301902
win32 allowed to fail manual
msys2-mingw32-autotools
passed #301901
win32
msys2-mingw32-meson

00:03:32