- Upgrade the version of GStreamer for Windows
This upgrades the Windows build to use the most recent version of
GStreamer. This is necessary to upgrade our GStreamer dependency.
- Stop shipping GStreamer binaries on Linux
The binary bundle of GStreamer that we package is not used to compile --
only to run layout tests. It's too old for the APIs that we are using
(as evidenced by needed 1.18 for WebRTC) and nowadays Linux
distributions carry a new version so it's unecessary for our build
machines. No longer using this binary bundle will allow us to upgrade
our GStreamer dependency -- which now has stricter checks that we
are using at least version 1.18.
- Upgrade media to use newer versions of GStreamer / GLib dependencies
Most tests were only being run for layout-2013, not for layout-2020.
This wasn't great since layout-2020 is now the default.
So this patch unifies the lists of included tests for both layouts.
For layout-2013 this implies adding css/css-content/, css/css-logical/
and css/css-masking/clip/.
For layout-2020 this implies adding several additional css tests, and
also tests like dom/, js/, html/, etc.
