Show XNote icon in collapsed threaded view

[froilo]

Moved from https://www.froihofer.net/bugzilla/show_bug.cgi?id=77

Feature request of a user:

Make it possible to see the XNote icon in the column in a collapsed thread, indicating that one or more XNote exists within in the thread?

I use the threaded view. Thunderbird Menu --> View --> Sort by --> Threaded

To compare, this functionality can be seen with Tags. For example: If a thread has 10 emails, and the 7th email is tagged "Important" and the Tag is Red, then the collapsed thread becomes red; when expanded, only the tagged email is red.

I notice that when the thread is collapsed, it turns yellow momentarily.