Resource tree counter does not update when string search is applied

[whyitfor]

What is the problem? (Here is where you provide a complete Traceback.)
When the "string" search function is used, the counter for collapsed notes on the Resource tree is not updated. This can confuse the user about how many results exist.

For example, when searching "localhost" on a filesystem, the "etc" node has +49, indicating 49 children:

In fact, there is only one child matching that search query:

Please provide some information about your environment.
This was observed running the GUI built off of d12b520.

If you've discovered it, what is the root cause of the problem?
There is no visual indicator as to how many of the children match the search query.

How often does the issue happen?
Every time.

What are the steps to reproduce the issue?
Se above.

How would you implement this fix?
Ideally, it should be clear to a user from glancing at the resource tree how many nodes match the search query.

Are there any (reasonable) alternative approaches?
N/A.

Are you interested in implementing it yourself?
Yes, once an approach is agreed upon!