This increase the safety of our build; external consumers
do no longer need to account for the `browser` field to
bundle bpmn-js (or otherwise bundle a Node shim, unintentionally).
* only register keyboard bindings that are backed by actual
editor actions
* rename BpmnKeyBindings -> BpmnKeyboardBindings for parity with
diagram-js@latest
* sub-class and override _keyboardBindings_ service provided
by diagram-js
* extend spec to verify default actions