Interpreting foreign functions call information as activity

Feature request

It'll be great if time between:
"HEC YY: stopping thread ZZZZZ (making a foreign call)" and
"HEC YY: running thread ZZZZZ" where YY and ZZZZZ are same between events and intepret as a single foreign call.

Activity diagram to show it as this thread is doing something foreign and this could be shown as separate coloured activity inside HEC graphs for YY execution unit.

This is a time spent somewhere else, but affecting us as we have to wait for it at this thread, so it's kind of activity albeit it is outside Haskell. It's time spent in foreign call which will be useful to be represented and measured.

Start by locating the event handling for “stopping thread ... (making a foreign call)” and the matching “running thread ...” message. Trace how these events become HEC activity diagrams, then define completion as showing the interval as a distinct foreign-call activity that can be measured.

Written by the indexing model from the issue text.