Fix incorrect forward declare keywords (#3107)

Mixups of class/struct keyword in forward declares. Doesn't seem to matter on MWCC, but causes name mangling mismatching on modern platforms.

include/JSystem/JAudio2/JAISeq.h

@@ -6,7 +6,7 @@
 #include "JSystem/JSupport/JSUList.h"
 
 class JAISeqMgr;
-class JAISoundChild;
+struct JAISoundChild;
 
 /**
  * @ingroup jsystem-jaudio

include/JSystem/JAudio2/JAISound.h

@@ -250,10 +250,10 @@ public:
 
 class JAISoundHandle;
 class JAIAudible;
-class JAIAudience;
+struct JAIAudience;
 class JAISe;
 class JAISeq;
-class JAISoundChild;
+struct JAISoundChild;
 class JAIStream;
 class JAITempoMgr;
 

include/JSystem/JAudio2/JAIStreamMgr.h

@@ -6,7 +6,7 @@
 #include "JSystem/JUtility/JUTAssert.h"
 
 class JAIStreamAramMgr;
-class JAIStreamDataMgr;
+struct JAIStreamDataMgr;
 
 /**
  * @ingroup jsystem-jaudio

include/JSystem/JAudio2/JASBank.h

@@ -4,7 +4,7 @@
 #include <dolphin/types.h>
 
 class JASChannel;
-class JASInstParam;
+struct JASInstParam;
 class JASWaveBank;
 
 namespace JASDsp {

include/JSystem/JAudio2/JASHeapCtrl.h

@@ -7,7 +7,7 @@
 #include <dolphin/os.h>
 #include <dolphin/os.h>
 
-class JASDisposer;
+struct JASDisposer;
 class JKRHeap;
 class JKRSolidHeap;
 

include/JSystem/JAudio2/JASSeqParser.h

@@ -3,7 +3,7 @@
 
 #include <dolphin/types.h>
 
-class JASTrack;
+struct JASTrack;
 
 /**
  * @ingroup jsystem-jaudio

include/JSystem/JAudio2/JAUSectionHeap.h

@@ -6,16 +6,16 @@
 #include "JSystem/JKernel/JKRDisposer.h"
 #include <bitset>
 
-class JAISeqData;
-class JAISeqDataMgr;
-class JAISeqDataUser;
-class JAIStreamDataMgr;
+struct JAISeqData;
+struct JAISeqDataMgr;
+struct JAISeqDataUser;
+struct JAIStreamDataMgr;
 class JASVoiceBank;
 class JAUBankTableLink;
 class JAUDisposer_;
 class JAUSectionHeap;
-class JAUSoundTable;
-class JAUSoundNameTable;
+struct JAUSoundTable;
+struct JAUSoundNameTable;
 class JKRArchive;
 class JKRSolidHeap;