Have a shared graph maximum value for all the event delay graphs

Currently, we use the maximum value of each thread to draw the event delay tracks. That means each event delay graph in a profile will have a different height scale. That makes it hard to compare with other graphs when we want to. Ideally we should use a global maximum value to scale all the event delay graphs.

Another possibly easy fix is to mark a threshold (eg 50ms which is our limit) with an horizontal line. Maybe we can even have 2 lines, one at 16ms (for animations) and one at 50ms (for hangs).

Note: Event delay tracks are also disabled by default for now. You can enable them by running `experimental.enableEventDelayTracks()` in the console.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-294)