Keep same frame selected when switching between JS and combined stacks

I tend to use JS stacks to locate sections of JS code with performance issues, and then need to switch to combined stacks to figure out exactly why they're slow. When I do that, I completely lose my context, and tend to have to do a new search for some relevant JS symbol to find my place again.

It would be _much_ easier if I could switch to combined stacks and keep the same frame selected (and ideally uncollapse trees enough to keep the same JS frames visible)

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-630)