* refactor: convert flyout_button.js to ES6 class
* chore: move some properties into constructor and add annotations for flyout base
* refactor: convert flyout_horizontal.js to ES6 class
* refactor: convert flyout_vertical.js to ES6 class
* refactor: convert flyout_base.js to ES6 class
* refactor: convert flyout_metrics_manager.js to ES6 class
* refactor: convert insertion_marker_manager.js to ES6 class
* refactor: convert metrics_manager.js to ES6 class
* refactor: convert grid.js to ES6 class
* refactor: convert input.js to ES6 class
* refactor: convert touch_gesture.js to ES6 class
* refactor: convert gesture.js to ES6 class
* refactor: convert trashcan.js to ES6 class
* chore: rebuild and run format
* chore: fix review comments
* chore: respond to PR comments