feat: read retrodeck dual-mode cores from es-de

RetroDECK listed every component standalone only. Azahar, Cemu, Dolphin,
MAME, melonDS, PCSX2 and PPSSPP also run through RetroArch: RetroDECK/ES-DE
es_systems.xml at 15e1b236 loads <name>_libretro.so beside each standalone
command, and the cores ship whole from the buildbot nightly
RetroArch_cores.7z (retroarch/component_recipe.json:250-262). Their
libretro layouts, Azahar's save-dir files among them, now reach the pack.

platforms/retrodeck.yml

@@ -44,6 +44,14 @@ standalone_cores:
 - vita3k
 - xemu
 - xroar
+dual_mode_cores:
+- azahar
+- cemu
+- dolphin
+- mame
+- melonds
+- pcsx2
+- ppsspp
 systems:
   triforce:
     files: