Apply containment to panels

Stanislav Lashmanovrequested to merge
slashmanov/panels-containment into master

What does this MR do and why?

This MR applies proper containment to panels in the panelled layout. It allows us to:

  1. Skip transform: translate() hacks to create stacking context
  2. Achieve better performance (panels don't cause redraws of the whole page)

No visual change expected.

How to set up and validate locally

  1. Enable paneled_view feature flag
  2. Open some drawers in the main panel
  3. Observe proper positioning of the drawer
  4. Open chat panel
  5. Observe no regressions

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