Fix persisted scoll position on glanceable hub

Scroll position should be persisted when going to edit mode and right
before leaving edit mode. And it should be reset once the UI is rendered
because the persisted scroll position has already been applied.

Test: atest CommunalEditModeViewModelTest
Test: manual; see test steps in bug
Fix: 419357924
Flag: EXEMPT bugfix
Change-Id: I2883677a06fbe17cfb7ec5c52c9f58e8cd0f4180