[Feature Request] New playlist management button to edit a manual scan from a existing manual playlist

To be clear this is something you can already do but it's on "accident" from the way RetroArch has bad cstring hygiene, and therefore can be "fixed" at any time in the future and the very useful feature disappear.

You can "refresh" a manual playlist in its playlist management, then back out of the screen twice and go to import content then manual scanner and all the options of the playlist "refreshed" will be filled, so you can tweak them without refilling them by hand.

I think this last part (without the obligatory useless "refresh") should be a full feature button. Not in the least because if someday RetroArch gets its act together with zeroing strings on every screen opening the 'hack' disappears, and also because how it's done now it's doing a extra scan for no reason.

I also think there should be a button to refresh all playlists that can be refreshed.

Start in RetroArch's playlist management and manual scanner screens, tracing how a refreshed manual playlist supplies options to the scanner. Define the new button flow so editing does not require an extra scan, and determine how a button for refreshing all eligible playlists should behave.