Update savestate ui behavior to match psx core

[birdybro]

• Add savestate auto increment slot feature like PSX core.
• Update savestate_ui.sv to match PSX behavior (including savestate hotkey behavior).
• Update Sys (minor update, inconsequential to core).
• Update status bit indexing to new method.

As discussed with @RobertPeip last week.

[birdybro]

Closing, I noticed a mistake...

[birdybro]

Actually, no, just bad eyesight apparently. Thought I forgot the OSD menu option.

[RobertPeip]

Thank you!