keyboard_listener library Null safety

TODO: Remove this file in the next breaking release, because implementation files should be located in the src folder, https://bit.ly/3fA23Yz.

Classes

KeyboardEventHandler

Enums

InputShortcut

Typedefs

CursorMoveCallback = void Function(LogicalKeyboardKey key, bool wordModifier, bool lineModifier, bool shift)
InputShortcutCallback = void Function(InputShortcut? shortcut)
OnDeleteCallback = void Function(bool forward)