Merge changes from apertis/v2020-updates into apertis/v2020

debian/changelog

-xorg-server (2:1.20.4-1+deb10u2+apertis1) UNRELEASED; urgency=medium
+xorg-server (2:1.20.4-1+deb10u2+apertis1) apertis; urgency=medium
 
-  * PLEASE SUMMARIZE remaining Apertis changes
+  * Merge from Debian buster-security. Remaining changes:
+    - Disable glamor and glxvnd in xwayland to avoid Xwayland
+      depending on big GL.
 
  -- Apertis CI <devel@lists.apertis.org>  Tue, 13 Jul 2021 15:34:23 +0000