* refactor: convert utils/coordinate.js to ES6 class
* refactor: convert utils/rect.js to ES6 class
* refactor: convert utils/size.js to ES6 class
* refactor: convert block_drag_surface.js to ES6 class
* refactor: convert block_dragger.js to ES6 class
* refactor: convert bubble_dragger.js to ES6 class
* chore: declare bubble property in the constructor
* refactor: convert bubble.js to ES6 class
* chore: clang-format
* chore(lint): lint and format