Eclipse should not re-evaluate a file compare window when closing it with save action

Migrated from: https://github.com/eclipse-jdt/eclipse.jdt.core/issues/3785#event-16706186357

It seems Eclipse peforms "if changes saved in compare window, re-evaluate comparison".

When comparing a large file (e.g., properties file) I often opt to Close file and (select Save changes on close) but Eclipse first saves file, re-evaluates changes (takes over ten seconds) and then closes the file, when it should obviously shortcut to closing when the changes will not be shown to the user due to the pending close action.

This improvement will help significantly when working with large files.

How to reproduce:

- open large file(s) in compare mode (one whose compare takes several seconds)
- make small change
- close file (compare window) and choose Save changes

Result: it should not re-evaluate compare when window is being closed with Save changes.