Save file location based on hash/title id

For example I have the same rom but with different filenames e.g. "Some Game.bin" and "Some Game (v1).bin"
Now RetroArch will create a save file for each file instead of sharing it.
I'd like to be able to have the save file location based on the hash of the rom, the title id (e.g. SLUS-01324), or the RetroAchievements hash maybe.
This way if I have the same rom with different filenames or if the rom got renamed the correct save file will be used.

Create a sub-directory per hash and store all relevant save data there.

saves/<hash>/sram.srm

saves/<hash>/slot1.mcr
saves/<hash>/slot2.mcr

Save states should also use a sub-directory based on the core library name.

states/mednafen_psx_hw_libretro/<hash>/0.state
states/mednafen_psx_hw_libretro/<hash>/autosave.state

Existing data should be imported if no save is in the new location yet.

Start by tracing RetroArch's existing save-file and save-state path handling. Compare the requested hash or title-ID layout with current filename-based behavior, including core library names and migration of existing data. Done means matching ROMs share the intended save data, states use the requested hierarchy, and old data is imported when the new location is empty.