Allow to toggle between showing samples and millisecond durations in call tree

Durations in milliseconds (even if they only approximate the real time) are easier to understand than the concept of samples (especially if you are not proficient in using sampling profilers).
I therefore propose to add the possibility to switch the sample counts to durations in the call tree (and associated view). An example of what this can look like is:

I'm happy to implement this feature.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-570)