Implement support for native keyboard layout

My take on the keyboard layout issue; prior attempts being !1270 (closed), !1640 (closed) and !695 (closed). My approach is to try to split keyboard handling in text input parts with game parts, and thus only the console, chat window and text boxes are affected, everything else should behave the same.

To do this, a new event (ev_text) is added and the handlers for the chat box, console and text boxes is changed to respect those new events. All other events and handlers behave the same.

Fixes https://github.com/STJr/SRB2/issues/444