Percentages in the sidebar are inconsistent

Some percentages in the call tree sidebar are relative to all visible samples, and some percentages are relative to the number of samples under the selected call node.

Example: Select `nsThread::ProcessNextEvent` on https://share.firefox.dev/3lFt8NF
The sidebar shows "Running samples: 29%" and then displays 80% and 20% for the categories underneath.

I don't have a proposal for what to do instead. But I want to point out that it can be confusing to newcomers.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-481)