Come up with a better "Scripts" rendering strategy for the JS Tracer view

> It may not be important for now but in case we use this to identify scripts in the future, this check will ignore any script events that come from self-hosted code. A better check is to maybe look for a non-null lineNo entry? That being said, I think there is a lot of value in having "self-hosted" events separate from the other script events in the self-time view.

_Originally posted by dpalmeiro in https://github.com/devtools-html/perf.html/pull/1422_

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-91)