Add sceResmgr, which is what the VSH uses to decrypt the XMB index

Found the cause of the red error screen the VSH ends on. Every resource load in
the boot succeeds - fonts, all the plugin RCOs, topmenu_icon.rco - and then:

  sceIoOpen(flash0:/vsh/etc/index_02g.dat) -> fd 8
  sceIoRead(8, 092a2d40, 496)
  sceIoClose(8)
  unresolved import sceResmgr/9dc14891, called from 'vsh_module'
  sceKernelExitDeleteThread(1)

index_02g.dat is the index of what the XMB displays, and it is encrypted (it
starts "PSPsysGP"). sceResmgr_9DC14891 decrypts it. There was no sceResmgr module
at all, so the call trapped, the index stayed encrypted, and the ScePafJob thread
building the top menu exited - a shell with everything loaded and nothing to show.

This adds the module and the three tags it needs (0x0B2B90F0/91F0/92F0, keys and
code 0x5C) to PrxDecrypter.

It is not the whole fix yet: pspDecryptPRX() tries decryption types 0, 1, 2, 5
and 6, and this needs type 9, which JPCSP passes explicitly. So the call is now
reached and fails cleanly with a logged error instead of trapping, but does not
yet decrypt. Type 9 is a variant of type 2 and is the next job; the notes in
docs/VSHBootInvestigation.md say where it is in JPCSP and how to check a port
(159 bytes out, starting "release:").

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01GZq8ZtJmFY7bkX5FVkr3P9

libretro/Makefile.common

@@ -812,6 +812,7 @@ SOURCES_CXX += \
 	       $(COREDIR)/HLE/proAdhocServer.cpp \
 	       $(COREDIR)/HLE/proAdhoc.cpp \
 	       $(COREDIR)/HLE/sceOpenPSID.cpp \
+	       $(COREDIR)/HLE/sceResmgr.cpp \
 	       $(COREDIR)/HLE/sceP3da.cpp \
 	       $(COREDIR)/HLE/sceMt19937.cpp \
 	       $(COREDIR)/HLE/sceMd5.cpp \