ui: Remove circular dependency related to public/index.ts

The circular dependency looks like this:
```
cycle: [
  'ui/tsc/public/index.js',
  'ui/tsc/frontend/debug_tracks/debug_tracks.js',
  'ui/tsc/frontend/debug_tracks/slice_track.js',
  'ui/tsc/frontend/debug_tracks/details_tab.js',
  'ui/tsc/frontend/slice_args.js',
  'ui/tsc/frontend/visualized_args_tracks.js',
  'ui/tsc/public/index.js'
],
```

The issue is that public/index.ts is becoming a bit of a god file,
which is a nightmare for circular deps.

This one was fixed by breaking the chain through public/index.ts, by
moving a lot of the track interfaces defined here into
frontend/tracks.ts instead, and then exporting them through
public/index.ts so plugins can use them.

This means a lot of the core files that use these track interfaces
can now just refer to core/tracks.ts, rather than depending on the
whole of public/index.ts.

Change-Id: I40768aaf758c79620b5a04a119d6d6c612eda49c