* Migrate core/events/events.js to ES6 const/let
* Migrate core/events/events.js to goog.module
* Migrate core/events/events.js to named requires
* clang-format core/events/events.js
* Migrate Blockly core to use getRecordUndo/setRecordUndo
* Update core/events.js to reflect latest guidance around exporting mutable fields