Clicking instant markers in the timeline causes a preview selection with a strange range

Profile: https://share.firefox.dev/3NdoSjR

Steps to reproduce:

1. In the Renderer thread timeline, find any "Composite" marker, and move your mouse slightly to the right so that you're over a "Render reason VSYNC" marker.
1. Click the "Render reason VSYNC" marker.

Expected results:
"Render reason VSYNC" is an instant marker, so I'd expect nothing to happen. Actually I wouldn't expect to see these types of markers in the timeline at all.

Actual results:
The preview selection is changed to a 159ms range centered around the clicked marker.

This was very confusing to me because I had intended to click a "Composite" marker, so I was expecting to get a selection that spans one composite. But the selection I ended up with was much longer than a composite and it made me wonder "What are we doing that's taking 159ms?"

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-547)