Update how duration and exclusive duration are calculated

[bizob2828]

Description

We have done work to remove the transaction from the segment(#2658). We are still attaching the root segment to every segment so it can update the exclusive time. Instead of having every segment update the root with a new time, I think we can just update the code to capture relative start/end times from its parent.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-335773

[bizob2828]

this is causing issues with losing context at times. I'm going to put this on the backlog

[jsumners-nr]

I think it is best to put this on hold for now. The duration timings are very tightly ingrained in the instrumentation flows. It will take some significant research to determine how they are currently handled in order to determine how to refactor them. I believe this is a bit too disruptive given the other significant refactoring we already have queued up for release.