[Feature Request] add scanner database check Loose+

Currently there is no way in the new hybrid scanner to select one of the built-in retroarch libretro databases but not use checksums for mapping a file to a game/label.

But there is a way using "Custom dat (Loose)", probably because that was part of the original manual scanner modes. This is immensely faster over a network (because retroarch is not streaming whole games to checksum), leading to a comical situation where if the user wants max scan speed and still get correct names for some sets or games, they download mame 300mb xml once and split them up by device (I did this, this is me).

I'd like at least one option for using the internal database and map if the current filename matches a filename in the selected retroarch rdb, map to the game name/label, all without a checksum. All my roms are named the same as the dumps used, except the hacks, I don't need to be babied but some sets (all arcade) need label database translations and some games need non standard characters that aren't in the file name because they're illegal in windows or something, so its good to use the libretro database mappings over None.

As youre at it I suspect the names could be a lot more... direct by abstracting that "also adding files of the right type(s) extensions if unmatched" to a single symbol that gets explained once in the help text

Something like:

Checksum (old strict)
Checksum+Ext (old loose)
Filename (new, no checksum, just the matched filenames, useful for arcade since it has bios zips)
Filename+Ext (new, no checksum, useful for sets with romhacks)
Custom dat (Checksum)
Custom dat (Checksum+Ext) (new)
Custom dat (Filename) (new)
Custom dat (Filename+Ext) (old misleading Custom dat(Loose))
Ext (old None)

And a text in the help that says:
"How the scan finds the game name in the database or dat, and the Ext denotes if unmatched files of correct extension gets added anyway (note this adds romhacks and in MAME may add unwanted bios/device zips). Not checking checksums is always faster on a slow disk or over a network."

(Edit shorted the help by turning None into Ext so the description of what it does matches the +Ext described).

Start by locating the new hybrid scanner and the existing Custom dat (Loose) handling, then trace how built-in RetroArch libretro databases map files and apply checksums. The work is done when the requested filename and extension-based modes, database mappings, and consolidated help text behave as described.