Add savestate slot count setting

[hrydgard]

This replaces #21082 .

Instead of new UI for setting auto load save state slots, we just limit that particular functionality to the first five.

We still default to 5 but support up to 30, I think that's a nice middle ground.

Translation strings added, and the Win32 menu works fine and updates correctly.

Also fixes a bug on the pause menu where the back button wasn't working to close the menu.

[Domiiniik]

Little UI issue: Currently selected savestate background UI overlaps with the new scrollbar UI making it look a little odd.
Also: "delete game config" is the only option here that is missing a UI icon making it look out of place ( in my opinion this option should be moved to the top bar of the game settings visible whole time to create\delete the config anyways or to the game info)

Screen_Recording_20260109_143103_PPSSPP.mp4

[hrydgard]

Yeah, I haven't decided where to move that yet.

I'm also considering removing the "currently selected savestate" selection if you don't have any keys bound to save/load state, because it does nothing in that case.

[Domiiniik]

Yeah, I haven't decided where to move that yet.

I'm also considering removing the "currently selected savestate" selection if you don't have any keys bound to save/load state, because it does nothing in that case.

Good idea, that is confusing