Enable experimental Portal/Pipewire/libcamera cameras by default

FF >= 116 allows to use cameras via Pipewire when enabling media.webrtc.camera.allow-pipewire. While it will likely still take a while until this is made the default, on most mobile devices it makes a lot of sense to enable it unconditionally, as cameras usually only work with libcamera, not via plain v4l2.

On top of that, FF >= 119 supports rotation, allowing for a correctly rotated camera picture.

Thus, this repo is probably a good place to carry a patch enabling this option.

The following example is taken on a PPP (obviously without patches from this repo):