Add onInfoGetText event to lua API

There is a popular Morrowind mod in development, Voices of Vvardenfell (VoV), which adds voice acting to the entire game: https://www.nexusmods.com/morrowind/mods/52279.

Previously, the mod only worked with MWSE, because OpenMW's Lua API lacked some of the necessary functionality. I have decided to add the required functionality in this PR which allows the mod to support OpenMW:

onInfoGetText event - fires whenever a new line of dialogue script appears on the dialogue menu.