fix: say which cores find their BIOS by content

DuckStation (bios.cpp:208, 397-427), SwanStation (host_interface.cpp:
136-194), rustation (lib.rs:107-160), FS-UAE (rommgr.cpp:92-151),
ares (firmware.cpp:116-136) and Altirra (uifirmwarescan.cpp:29-113)
scan a folder and identify firmware by hash; Ymir does in its
standalone build only. FS-UAE still opens rom.key by name
(rommgr.cpp:1397-1498). The export then stops writing their labels
into platform lists: Batocera's psx block goes from 106 entries to 10,
and System.dat's scph5000.bin keeps its own hashes.

emulators/rustation.yml

@@ -9,6 +9,7 @@ upstream_commit: "1daf4faaade3c0fd1e9deace8e309e91303f1b46"
 core_version: "v1"
 display_name: "Sony - PlayStation (Rustation)"
 cores: [rustation]
+found_by: content
 systems: [sony-playstation]
 
 notes: >