Blender Git Loki

UI: Add light count to viewport statistics

Even though lights were part of `SceneStats`, they were not used when
rBfd10ac9acaa0 was committed.

This patch adds the light count back into the statistics. When a light is
the active object, it will display the total number of lights in the
scene, as well as how many lights are currently selected.

{F10141354}

Reviewed By: #user_interface, Severin, Blendify, harley

Maniphest Tasks: T88512

Differential Revision: https://developer.blender.org/D11387