[Proposal]Profiling memory usage per isolate

### Use case

I would like to profile memory usage of my app per isolate. Currently in profiler I can't find a way to separate allocations per each isolate. I tried to do it programatically by connecting to the websocket of the profiling session, but even after a few attempts to get allocations per isolate, I don't really trust the results. I'm using flutter_isolate and background_locator plugins which basically create their own FlutterEngine.

### Proposal

I'd like to have a combo box in the profiles which separates allocations for each isolate.