Compare profiling results

[firelizzard18]

Is your feature request related to a problem? Please describe.
While discussing #1685, @jmaister informed me that go tool pprof can create a diff diagram between two CPU/memory profiles, and he would like to see this feature added to the extension.

This would allow users to easily see the performance impact of changes they make.

Describe the solution you'd like
Some mechanism to select two performance profiles for comparison. The implementation will be largely the same as the basic profile display tool (which is not yet implemented).

Describe alternatives you've considered
Pretty much just doing it manually.

[hyangah]

pprof tool stores temporary data in PPROF_TMPDIR, but that's pretty unstructured dump of collected profiles (the name encodes some info time/profiletype/collection method hints...). Actively managing collected profiles can be convenient.

How about having a temporary directory (or give a user to configure the directory) and store profiles there? Schema design work is still necessary. Having FileSystemProvider around it and providing users with ability to navigate/select/delete them may be cool (I don't know how :-P)

Another idea is: to persist data across sessions, workspaceState vscode.Memento may store the directory location. If it exists, use it. If it's gone, reset.

[firelizzard18]

I'm wondering how to handle the UX for persistent profiles. I can come up with a persistent place/way to put them, but users probably don't want profiles to stay around indefinitely.