Fix unresponsive textarea from addon-event

[lonyele]

Issue: Fixes #6936

What I did

Problem

From getDerivedStateFromProps, comparing some props and some state(always undefined) always initializes state which makes changing on textarea unresponsive.

Implementation

• Assign payload value to prevPayload
• Using lodash isEqual to properly compare changing props' payload and state's prevPayload

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps? No
• Does this need an update to the documentation? No

If your answer is yes to any of these, please make sure to include it in your PR.

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[shilman]

see comment

[ndelangen]

@lonyele I invited you to the github org. 👍

[lonyele]

@shilman just ping for the comment. I'd like to migrate addon-event to typescript...

[lonyele]

@ndelangen hm.. same goes here. Color is changed but it is not expected. I'll investigate this too