MultiSelect: expose the currently selected option item

[dandohotaru]

There is no guarantee in receiving a response in GitHub Issue Tracker, If you'd like to secure our response, you may consider PrimeNG PRO Support where support is provided within 4 business hours

I'm submitting a feature request

[ ] bug report => Search github for a similar issue or PR before submitting
[x] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

Current behavior
For the time being the p-multiSelect has various events among them onChange

a Callback to invoke when value changes
event.value: Current selected values

Expected behavior
Besides onChange that returns all the selected items, it would be great if the current selected item could be reflected as well in the api

What is the motivation / use case for changing the behavior?
For situations where selecting a particular item should trigger some specific actions down the line

• Angular version:
  5.0.0

• PrimeNG version:
  5.0.2