feat(libSceUserService): report the keyboard type of the system language

sceUserServiceGetKeyboardType now returns the keyboard type of the configured
system language from the repository owner's table (languages 0 to 29), with 20
(US English) for a language outside it. The input variants stay 0, the only
value the table gives for Japanese and Traditional Chinese.

sceConvertKeycodeGetImeKeyboardType takes the PS4 client rule from the title ID
prefix (CUSA is PS4); a missing or custom ID is treated as PS5. Tests walk the
owner's table through both calls and the title ID cases; both debt entries
updated.

docs/dev/debt/libSceConvertKeycode.md

@@ -3,4 +3,4 @@
 ### Functional
 
 - [sceConvertKeycodeGetVirtualKeycode](../../../core/libs/prx/libSceConvertKeycode/Export.cpp) and `sceConvertKeycodeGetCharacter`: layouts 31–39 throw until the guest platform and compiled SDK version are exposed. `GetVirtualKeycode` also throws for version-dependent Y/Z mappings in layouts 2, 3 and 12. Mapping tables and modifier behavior are recovered; no SDK version is guessed.
-- [sceConvertKeycodeGetImeKeyboardType](../../../core/libs/prx/libSceConvertKeycode/Export.cpp): implemented exactly as the repository owner (boykopovar) specified the UserService keyboard type (plus the Japanese variant for type 37 and the Traditional Chinese variant for type 39) to IME keyboard type table, the SDK compatibility rules (38 becomes 4 for PS5 SDK below 0x06000000 or PS4 SDK below 0x10000000; 39 becomes 29 for PS5 SDK below 0x08000000 and for every PS4 client), the error codes and the unmatched-type result (success, IME type 0). The PS4/PS5 client rule assumes a PS5 process because `sceKernelIsPs4Process` is unimplemented and AnyPS5 runs PS5 processes. UserService has no stored keyboard setting yet, so every user reports the US-English default keyboard type 20 and the function returns IME type 4 until one is stored (see libSceUserService.md).
+- [sceConvertKeycodeGetImeKeyboardType](../../../core/libs/prx/libSceConvertKeycode/Export.cpp): implemented exactly as the repository owner (boykopovar) specified the UserService keyboard type (plus the Japanese variant for type 37 and the Traditional Chinese variant for type 39) to IME keyboard type table, the SDK compatibility rules (38 becomes 4 for PS5 SDK below 0x06000000 or PS4 SDK below 0x10000000; 39 becomes 29 for PS5 SDK below 0x08000000 and for every PS4 client), the error codes and the unmatched-type result (success, IME type 0). The PS4/PS5 client rule reads the title ID prefix from `param.sfo` or `param.json` (`CUSA` is PS4); a missing or custom ID, as in homebrew, is treated as PS5. Reliable detection inspects the original `eboot.bin`, which only the relinker reads, so it is not done. UserService reports the keyboard type of the configured system language, so the function returns the owner's IME type for that language (see libSceUserService.md).