Display the marker start and end times in the tooltip

Currently our marker's tooltips look like this:

Look especially at the first line: there's the duration, and the name.

I think we should have the start time too. I miss this a lot when inspecting profiles.
It may be also interesting to show the end time as well. I didn't feel the need so much about it myself but why not. ([this also requested on bugzilla](https://bugzilla.mozilla.org/show_bug.cgi?id=1471229)).

I don't have a good idea about how to display this extra information though. Any idea ?

Also don't forget the case of the markers where we don't know the start or the end times (markers that start/end outside of the range).

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-53)