Add support to external controllers battery level

[shinsei_kaburagi]

Allow me to see how much battery my external controller has (ex: Dualsense) on the steam deck UI.

For exemple in desktop mode i can see it, but not on steam deck mode

[Moskeeto]

This is currently a feature in the Steam Deck beta.
https://store.steampowered.com/news/app/1675200/view/4177730135016134611

"Show battery information for connected Bluetooth devices under Settings->Bluetooth and in the Quick Access menu."

[BeardWarrior]

Not all controllers seem to be supported for battery level display. I can see battery levels for my Xbox One controller, but not for my DualSense or Switch Pro controllers. I agree that it would be nice to have more comprehensive support for battery display, expectation since the levels are exposed and visible on desktop mode.

[shinsei_kaburagi]

I think this feature finally made it to the stable channel

But I haved tested with my dualsense, and still does not show the battery level