Display the fetched JS files in the source view

[canova]

Once we have a way to request source code and source map from Firefox with #5110, we can show that in the source view.

Looking at this place, it appears that we already support JS and TS file formats. So I don't think we need to work on bringing the syntax support for JS: https://github.com/firefox-devtools/profiler/blob/662dc4aef2da516b0099bfe9c94c7ffdf34b5200/src/components/shared/SourceView-codemirror.js#L52-L61

This issue is a part of #3741.

┆Issue is synchronized with this Jira Task