Add a button to open the Steam screenshot folder

[Kabouik]

Having a button to open the screenshot folder for individual games would be convenient, especially for Steam screenshots (F12) since they are stored outside the game directory. I reckon it cannot be done for screenshots taken using the game built-in shortcut since the folder would not be standard, but for Steam games and F12 screenshots, there should be a folder specific to the game ID.

The button could be added in this toolbar:

I think GOG Galaxy has a similar screenshot feature but it is not relevant for Linux.

[Kabouik]

Excellent, thanks @tkashkin!