Search freezes UI if "Show only most nested match" filter is enabled #4337

Found while testing #4236.

Regression originating initially from 0474b01 / eclipse-platform/eclipse.platform.text#144, reported in eclipse-platform/eclipse.platform.text#187 and (probably) not fully fixed eclipse-platform/eclipse.platform.text#189 or appearing again after some other change.

If "Show only most nested match" filter is enabled, search query that finds many matches freezes UI for a very long time.

To reproduce, clone https://github.com/iloveeclipse/java-project-generator/compare/issue_3720 branch, import project, run "Main" , refresh the project and search in the project for "a" character. In the current case we will have ~1.000.000 matches in 20.000 files. UI will freeze for ~10 minutes (depending on HW).

I plan to push the fix.