Log Message:
picom: update to version 8.

pkgsrc changes:
- Restore patch-src_backend_gl_gl__common.c from the previous "compton"
  package. It is smaller and better explains why the patch is needed.
- drop dependency on libxdg-basedir, dropped by upstream.

Upstream new feature & improvements
- You can now use the time variable in window shaders to get a timestamp.
- --max-brightness, which allows you to dim windows that are too bright.
- Automatic configuration file reloading after it's changed.
- A lot of the artifacts seen with blur and use-damage enabled are fixed.
- _NET_WM_BYPASS_COMPOSITOR property are now handled.
- Completely transparent windows won't have a blurred background anymore.
- Improved fullscreen window detection.
- Various improvments to the inverter.sh script
- wintype notify has been renamed to notification to match the EWMH names
- (also various bug fixes)