feat(message): add SMsg functions

[heinermann]

Exists in WoW but I think it's only used by Diablo II.

I can't be bothered to slog through testing it and we won't be using it, so just putting it up for visibility in case the D2 people want it.

Ordinal	Name	Implemented	Tested
411	SMsgDestroy	✓
412	SMsgDispatchMessage	✓
414	SMsgRegisterCommand	✓
415	SMsgRegisterKeyDown	✓
416	SMsgRegisterKeyUp	✓
417	SMsgRegisterMessage	✓
418	SMsgPopRegisterState	✓
419	SMsgPushRegisterState	✓
420	SMsgRegisterSysCommand	✓
511	SMsgBreakHandlerChain	✓
512	SMsgUnregisterCommand	✓
513	SMsgUnregisterKeyDown	✓
514	SMsgUnregisterKeyUp	✓
515	SMsgUnregisterMessage	✓
517	SMsgSetDefaultWindow	✓
518	SMsgGetDefaultWindow	✓
519	SMsgUnregisterSysCommand	✓
582	SMsgSetDefaultWindowRect	✓
583	SMsgGetDefaultWindowRect	✓

SMsgDoMessageLoop and SMsgGetGenericWndProc are excluded because they are both (a) not used and (b) extremely tied to Windows APIs, more than just a single call or type.

I'm aware that a 64-bit compile will cast the HWND to 32 bits but SEvt on 64-bit WC3 uses 32-bit arguments...