Dynamic properties are deprecated in PHP 8.2

Patch is attached.

I'm looking at this in the Backdrop version, where a contributor has made the following comment:

> I don't agree with the fix there. It makes more sense to define property $tags, since it's integral to the functioning of the class.

There is a PR on the issue to do so in Backdrop, which could easily be ported here for Drupal 7 if you agree:
https://github.com/backdrop-contrib/search_api/issues/57

Thanks a lot for reporting this issue, and especially for already providing a patch!

However, I agree with @argiepiano in the Backdrop PR: We should just declare that property, especially if it’s already set in the constructor.
Patch attached, please test/review!

drunken monkey → credited argiepiano → .

Merged. Thanks again, everyone!

Automatically closed - issue fixed for 2 weeks with no activity.