[gst-plugins-bad] Enable D3D12 support

[benjamin-otte]

I'm currently in the process of adding D3D12 support to GTK's Windows build (relevant GTK MR) and while enabling GStreamer I noticed that our msys2 CI is failing.

While tracking this down I found out that D3D12 support in gst-plugins-bad is explicitly disabled since commit 87d099a which claims:

all others are new and are not supported on Windows or mingw specifically

And if the GStreamer plugins do require those extra features: Could you make them work?

Otherwise I'll have to add a "d3d12-gstreamer-support" option to my GTK MR to make our CI pass and I don't want to.

[lazka]

The current result is:

../gst-plugins-bad-1.24.9/sys/d3d12/meson.build:58:4: ERROR: Problem encountered: d3d12 plugin supports only MSVC build

due to https://gitlab.freedesktop.org/gstreamer/gstreamer/-/blob/6575d1de8eec1cfbd8ec87f1edef3890854a59ed/subprojects/gst-plugins-bad/sys/d3d12/meson.build#L58

This restriction was lifted with https://gitlab.freedesktop.org/gstreamer/gstreamer/-/commit/bbdfa00b7b3b7febaea2faf97eb7982cf21031ae?page=2 in main (plus some follow up commits), so maybe it could be backported.

[lazka]

There are various conflicts, so I've given up for now