Handle clicking the activity graph for multiple selections of threads

For issue #88 of adding multiple selection, PR #2706 is not handling sample clicking in the activity graph and stack graph.

This work would need to create a mapping from the original thread call nodes to the merged thread call nodes, and take the sample, and map it to the merged space. I'm not sure it's worth changing the rendering of the ActivityGraph or not, as the filtering pipelines are different.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-298)