CppIncludesFilter not reliable

Apply https://codereview.qt-project.org/c/qt-creator/qt-creator/+/459386 patch (patchset 6) and do:

1. Run Creator and open a session containing Creator project.
2. Wait until "Parsing C/C++ Files" finishes.
3. Open locator.
4. Wait until locator spinner disappears and hit space once. Notice HIT COUNT printout.
5. Repeat step 4 few times. Notice that HIT COUNT is always the same.
6. Close Creator.

When all these steps are repeated, HIT COUNT is different on each Creator run. To be precise: for 1st Creator run it's constant, for 2nd Creator run it's still constant, but HIT COUNT from 1st run is different from 2nd run.

I my case, I got the following printout on 1st run:

HIT COUNT: 6592 time: 932 entry list written to CppIncludesFilter.txt
HIT COUNT: 6592 time: 934 entry list written to CppIncludesFilter.txt

2nd run:

HIT COUNT: 6586 time: 933 entry list written to CppIncludesFilter.txt
HIT COUNT: 6586 time: 932 entry list written to CppIncludesFilter.txt

3rd run:

HIT COUNT: 6679 time: 934 entry list written to CppIncludesFilter.txt
HIT COUNT: 6679 time: 929 entry list written to CppIncludesFilter.txt

The difference in hit count may be even about 100 files.