loadso: library handles are now SDL_SharedObject* instead of void*.

Improved the SDL_loadso.h documentation a little, too.

Fixes #11009.

src/test/SDL_test_memory.c

@@ -34,7 +34,7 @@ static bool s_unwind_symbol_names = true;
 #include <dbghelp.h>
 
 static struct {
-    HMODULE module;
+    SDL_SharedObject *module;
     BOOL (WINAPI *pSymInitialize)(HANDLE hProcess, PCSTR UserSearchPath, BOOL fInvadeProcess);
     BOOL (WINAPI *pSymFromAddr)(HANDLE hProcess, DWORD64 Address, PDWORD64 Displacement, PSYMBOL_INFO Symbol);
     BOOL (WINAPI *pSymGetLineFromAddr64)(HANDLE hProcess, DWORD64 qwAddr, PDWORD pdwDisplacement, PIMAGEHLP_LINE64 Line);