[4.2][Debug] Add benchmarking for filters.

[sfadschm]

This PR adds timers for the before and after filters.

During #4863, I found that significant gaps in the timeline can be produced by the filters.
As far as I could find, these are the only parts missing in the benchmarking.

For now, I opted to

• start the timers in CodeIgniter4::handleRequest,
• not divide the filter timers further into the individual filters.

In the current state, the Filters timer is displayed even if no filters are defined for the $position, this is not really the best solution in my opinion, however, $filters->run is called each time anyway, so why not log those ms, too.

The alternative would be to run $filters->initialize($uri) in handelRequest and then check the $filters->filtersClass property for defined filters.

On another note, I would like to explicitly time each running filter, too. However, the only way to achieve this currently would be to use the timer() helper in Filters::run() or to inject Services::timer into the Filters. Not sure if any of these options is feasible right now.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Conforms to style guide

[sfadschm]

After considerations, this is a functioning and easy implementation, but using an own collector or such might be more useful. Will think about useful ways.

[sfadschm]

Updated to not use the helper workaround for general benchmarking.