temp/libcamera: Enable virtual pipeline

Analog to a recent change in Fedora:
https://src.fedoraproject.org/rpms/libcamera/pull-request/14

This change allows to easily create virtual cameras, which is helpful
for testing and debugging purposes, both for system components like Mesa
and Pipewire as well as various apps.

The virtual cameras can be enabled by:
```
cd /usr/share/libcamera/pipeline/virtual
cp virtual.yaml.example virtual.yaml
systemctl --user restart pipewire
```

Using the test option allows to keep the arch dependent automatic pipeline
selection in place. It also enables building of the vimc pipeline -
which is very small - and all tests, however those don't get included
into the packages.

The new dependency, libyuv, is very small and already installed by
default for DEs like gnome-mobile.

Part-of: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/6567
[ci:skip-build]: already built successfully in CI

temp/libcamera/APKBUILD

@@ -3,7 +3,7 @@
 pkgname=libcamera
 _pkgver=0.5.0
 pkgver=9999$_pkgver
-pkgrel=0
+pkgrel=1
 pkgdesc="Linux camera framework"
 url="https://libcamera.org/"
 arch="all"
@@ -24,6 +24,7 @@ makedepends="$depends_dev
 	libevent-dev
 	libpisp-dev
 	libunwind-dev
+	libyuv-dev
 	linux-headers
 	meson
 	py3-jinja2
@@ -80,6 +81,7 @@ esac
 
 build() {
 	abuild-meson \
+		-Dtest=true \
 		-Dv4l2=true \
 		-Dwerror=false \
 		. output