Supporting importing Event Tracing for Windows traces (ETW, .etl, .etlx?)

ETW supports doing 8kHZ CPU time sampling which is quite valuable for diagnosing problems that are shorter lived. Most UIs for viewing the produced .etl files are not very good so being able to view them in the Firefox profiler would be pretty valuable.

https://github.com/microsoft/perfview has a speedscope exporter and there's some more information on importing the traces here: https://github.com/jlfwong/speedscope/issues/217.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-429)