windows: directsound should also map audio device GUIDs to proper names.

Moved this code from winmm into core so both can use it.

DirectSound (at least on Win10) also returns truncated device names, even
though it's handed in as a string pointer and not a static-sized buffer.  :/

src/audio/directsound/SDL_directsound.c

@@ -155,7 +155,7 @@ FindAllDevs(LPGUID guid, LPCWSTR desc, LPCWSTR module, LPVOID data)
 {
     const int iscapture = (int) ((size_t) data);
     if (guid != NULL) {  /* skip default device */
-        char *str = WIN_StringToUTF8(desc);
+        char *str = WIN_LookupAudioDeviceName(desc, guid);
         if (str != NULL) {
             LPGUID cpyguid = (LPGUID) SDL_malloc(sizeof (GUID));
             SDL_memcpy(cpyguid, guid, sizeof (GUID));