GX2: Rework GX2Set*UniformReg

- Use cafeExportRegister() instead of legacy export
- Submit as a single PM4 packet
- Add logging for the special case of the size parameter (not sure if this is used by any game?)
- Add some extra validation and logging which may be helpful to homebrew devs

src/Cafe/OS/libs/nn_act/nn_act.cpp

@@ -543,8 +543,6 @@ void nnActExport_GetDefaultAccount(PPCInterpreter_t* hCPU)
 void nnActExport_GetSlotNo(PPCInterpreter_t* hCPU)
 {
 	// id of active account
-	// uint8 GetSlotNo(void);
-	cemuLog_logDebug(LogType::Force, "nn_act.GetSlotNo()");
 	osLib_returnFromFunction(hCPU, 1); // 1 is the first slot (0 is invalid)
 }