Draft: brightnesscontrol: add support for ambient light devices supported by iio-sensor-proxy

All my devices do not support ambient light, so tests welcome!

To test, run

qdbus-qt5 org.kde.Solid.PowerManagement /org/kde/Solid/PowerManagement/Actions/BrightnessControl setBrightnessMode 1

If your device doesn't have a supported ambient light sensor, run autotests/mockiiosensorproxy.py with root permission to create a mocked dbus interface.

Ref:

• https://gitlab.gnome.org/GNOME/gnome-settings-daemon/-/commit/afd1ec179f8f497a8068fc413102c2ba1b42a26f
• https://gitlab.gnome.org/GNOME/gnome-settings-daemon/-/commit/bbdef3f87c6a16588cc05dfd798e610b327ebfbd
• #21

"Same river" series:

• Automatic screen brightness reacts on sensor jitter
• Max brightness level stuck at dim setting intensity after inactivity before suspend
• (Pinephone)Screen auto brightness control and low ambient luminosity
• Automatic brightness too abrupt
• Improve heuristics for automatic brightness control
• Automatic brightness changes it too often
• Make the automatic display brightness control function more visible