GUI: U32: Begin making TTS take in U32Strings for saying

Only for strings without an explicit action. The first level takes in a u32 string, encodes it, and passes it along further with the default action

- For gui widgets, the strings are passed in as native u32 strings.
- For everything else, they are being converted to u32 by Common::convertToU32... and then being passed along

backends/graphics/opengl/opengl-graphics.cpp

@@ -857,7 +857,7 @@ void OpenGLGraphicsManager::osdMessageUpdateSurface() {
 			ConfMan.getBool("tts_enabled", "scummvm")) {
 		Common::TextToSpeechManager *ttsMan = g_system->getTextToSpeechManager();
 		if (ttsMan)
-			ttsMan->say(Common::convertFromU32String(_osdMessageNextData));
+			ttsMan->say(_osdMessageNextData);
 	}
 #endif // USE_TTS
 	// Clear the text update request