Fix preview not updating on grid reset (2/3)

Add GridInteractor as a dependency for PreviewWithThemViewModel. Track
grid selected option changes, and factor it into preview view model's
workspaceUpdateEvents, which informs ScreenPreviewBinder to update.

This change does start up the Grid interactor, repository, and snapshot
restorer on app start, but does not cause noticeable delay.

Flag: EXEMPT bug fix
Bug: 323961452
Test: manually verified
Test: GridInteractorTest still passes
Change-Id: I60f5b5ff3271b4a5b6d533d31ba86acbfffe0f5b