Fix used lifecycle hook for initial component property checks

[oliverschuerch]

post-icon and other components throw an error, even when a required property is set.

Tasks

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1. Call all property checkNonEmpty check in componentDidLoad hook instead of componentWillLoad.
2. Test if the error is gone.
3. Cherry pick #3153 on main (or v8, depending on the branch it's getting merged into) #3687
   v8 +1

We can see the same error also in our documentation e2e tests:

Use these to test if the fix works.