Rejigs the typing relationship so that use of a typer is not strongly implied by the interface.

Simultaneously implements typing on the MSX by direct insertion into the key buffer.

Machines/KeyboardMachine.cpp

@@ -27,3 +27,6 @@ void Machine::reset_all_keys(Inputs::Keyboard *keyboard) {
 Inputs::Keyboard &Machine::get_keyboard() {
 	return keyboard_;
 }
+
+void Machine::type_string(const std::string &) {
+}