Feature: input can now use overwrite mode when toggled with insert key (#735)

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

include/ftxui/component/component_options.hpp

@@ -177,6 +177,7 @@ struct InputOption {
   std::function<Element(InputState)> transform;
   Ref<bool> password = false;  /// < Obscure the input content using '*'.
   Ref<bool> multiline = true;  /// < Whether the input can be multiline.
+  Ref<bool> insert = true;     /// < Insert or overtype character mode.
 
   /// Called when the content changes.
   std::function<void()> on_change = [] {};

include/ftxui/component/event.hpp

@@ -55,6 +55,7 @@ struct Event {
   static const Event TabReverse;
   static const Event F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12;
 
+  static const Event Insert;
   static const Event Home;
   static const Event End;