fix: give AdvanceMAME's sets both dir_rom folders

EmuELEC starts AdvanceMAME for arcade, mame and cps1-3 (es_systems.json).
advmame.sh sets dir_rom to /storage/roms/arcade for arcade and keeps
/storage/roms/mame for every other system (advmame.sh:26-30, 80), so an
arcade set is read in both. A binding gave each entry one place: an entry
launched both for a system a record names and for one it does not now
takes the place of each, in the pack, the manifest and verify. A system
the platform's list or machines put the entry under stands for the
entry's own ids, so XRoar's coco3.rom stays in RetroBat's bios/coco alone.

The AdvanceMAME sets are filed under arcade as well as their board.

A second-pass copy outside the BIOS tree now carries its layout path and
resolves by it, as the first pass does: EmuELEC's roms/mame/stvbios.zip
took bios/Arcade/MAME's set by that tail, roms/arcade/stvbios.zip the
Arcade/Arcade one.

Manifests: EmuELEC gains the 29 sets in roms/arcade, each the file
roms/mame holds. roms/mame/stvbios.zip changes from bios/Arcade/MAME to
bios/Arcade/Arcade/stvbios.zip, the copy the entry resolves to. Nothing
else moves.

scripts/packextras.py

@@ -1545,6 +1545,11 @@ def _collect_emulator_extras(
                     extra["system_dir"] = f["system_dir"]
                 if f.get("unprefixed"):
                     extra["unprefixed"] = True
+                # A copy placed outside the BIOS tree resolves by its layout
+                # path alone, as the first pass does: EmuELEC's
+                # roms/mame/stvbios.zip took bios/Arcade/MAME's set by that tail.
+                if f.get("layout_path"):
+                    extra["layout_path"] = f["layout_path"]
                 extra["claim_order"] = (2, 0, emu_name)
                 if _take(extra, full_dest, seen_dests, taken):
                     extras.append(extra)