Convert anonymous to arrow functions

src/display/focus.js

src/display/highlight_worker.js

src/display/mode_state.js

src/display/operations.js

src/display/scroll_events.js

src/display/scrollbars.js

src/display/selection.js

src/edit/CodeMirror.js

src/edit/commands.js

src/edit/deleteNearSelection.js

src/edit/drop_events.js

src/edit/fromTextArea.js

src/edit/global_events.js

src/edit/key_events.js

src/edit/main.js

src/edit/methods.js

src/edit/mouse_events.js

src/edit/options.js

src/input/ContentEditableInput.js

src/input/TextareaInput.js