Fix MSVC compiler and linker errors

- Fix struct/class forward declaration mismatches (JAIAudience, JASTrack) causing different MSVC mangled names and unresolved symbols
- Add jsystem_stubs.cpp with stubs for JASHeap, JASVoiceBank, J3DShapeTable, JAUSection, JHICommBuf, HIO/HIO2, JOR

src/d/actor/d_a_b_ds.cpp

@@ -5703,4 +5703,7 @@ actor_process_profile_definition g_profile_B_DS = {
     fopAc_CULLBOX_CUSTOM_e,
 };
 
+cXyz daB_DS_c::getHandPosR() { return mHandPos[1]; }
+cXyz daB_DS_c::getHandPosL() { return mHandPos[0]; }
+
 AUDIO_INSTANCES;