fix(pubsub): externalize PubSub event to SlickEventData to stop bubbling

[ghiscoding]

• add a way to externalize the Custom Event used internally by the PubSub Service so that the user could call preventDefault() on the SlickEventData as well, for example the CompositeEditor demo has the event onBeforeEditCell and if the user calls the preventDefault even on the SlickEventData (e.g. with Aurelia or Angular), then the SlickGrid .notify should receive a returnValue of false because when the PubSub calls the dispatchEvent with an event that was prevented, then the returnValue will be false, see MDN for reference: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/dispatchEvent#return_value
• this fixes an issue that I've opened on Aurelia project via this issue comment and Aurelia-Slickgrid PR that was a temp fix, the PR here will fix it in a proper and correct way to handle the event

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.8%. Comparing base (a2cfbc6) to head (4e0e64f).

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1444     +/-   ##
========================================
+ Coverage    99.8%   99.8%   +0.1%     
========================================
  Files         199     199             
  Lines       21617   21621      +4     
  Branches     7235    6967    -268     
========================================
+ Hits        21553   21557      +4     
- Misses         58      64      +6     
+ Partials        6       0      -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.