fix(hwaccel): add libmfx-gen1.2 to Intel Arc setup for QSV support

Add missing libmfx-gen1.2 package to _setup_intel_arc() for both
Ubuntu and Debian. Without this package, QSV hardware acceleration
fails with 'Error creating a MFX session: -9'.

The package was already present in _setup_intel_modern() (Gen9+)
but missing from the Arc GPU path.

Closes #11701

misc/tools.func

@@ -3595,6 +3595,7 @@ _setup_intel_arc() {
     $STD apt -y install \
       intel-media-va-driver-non-free \
       intel-opencl-icd \
+      libmfx-gen1.2 \
       vainfo \
       intel-gpu-tools 2>/dev/null || msg_warn "Some Intel Arc packages failed"
 
@@ -3621,6 +3622,7 @@ _setup_intel_arc() {
       intel-media-va-driver-non-free \
       ocl-icd-libopencl1 \
       libvpl2 \
+      libmfx-gen1.2 \
       vainfo \
       intel-gpu-tools 2>/dev/null || msg_warn "Some Intel Arc packages failed"
   fi