feat: list retrodeck standalone emulators

platforms/retrodeck.yml

@@ -25,6 +25,25 @@ cores:
 - vita3k
 - xemu
 - xroar
+standalone_cores:
+- azahar
+- cemu
+- dolphin
+- duckstation
+- gzdoom
+- mame
+- melonds
+- openbor
+- pcsx2
+- pico-8
+- ppsspp
+- primehack
+- rpcs3
+- ruffle
+- solarus
+- vita3k
+- xemu
+- xroar
 systems:
   triforce:
     files: