Determine which DevTools windows should allow multiple tabs per tool window

Multiple tabs per tool window will appear if there are multiple apps running. This is appropriate for the inspector tool window since each app running could have different widget trees. But I don't think this applies to every page of DevTools, so an audit is appropriate here.

Inspector tool window:
- Multiple tabs possible, one for each app

Other DevTools (performance, CPU profiler, memory, etc):
- Multiple tabs possible, one for each app

Deep links:
- Only one tab
- Should not be associated with an app, i.e. VM service URI should not be appended

Extensions:
- Only one tab
- Should not be associated with an app, i.e. VM service URI should not be appended

@kenzieschmoll is the above correct? I don't know if we need to prioritize cleaning up multi-app support immediately (as it doesn't seem to be used much), but currently I suspect deep links and extensions should be changed to not append VM service URI.