[4.3] Backport of Smart Search: Fixing taxonomy filter handling

[obuisard]

Backport of PR #39751 that was merged into 5.0.
This should have been included in 4.3 and was overlooked.
Our sincere apologies to the author of the original PR, Hannes @Hackwar.

Summary of Changes

When the taxonomies were refactored to be a nested set, this part was overlooked. This means that nested taxonomies in filters don't work.

Testing Instructions

1. Create an article in a category which is at least on the second level.
2. Create a filter which only searches in that articles parent category.
3. Go to the frontend and search for a word in that article. You will get the article as result.
4. Add &f=[filter-id] to the URL to only show results from our category.
5. Notice that you get no result at all!
6. Apply changes.
7. Only the article appears again.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[wilsonge]

Just FYI backporting things like this is going to cause you major merge conflicts once this is merged and you need to merge 4.3-dev into 5.0-dev

[Sabine-2023]

I have tested this item ✅ successfully on b1c9c91

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[ceus1984]

I have tested this item ✅ successfully on b1c9c91

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[richard67]

RTC

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[sdwjoomla]

Thanks @Hackwar