[SB][RONs] Support multiple ongoing activity chips.

This CL updates the left side of the status bar to show up to 2 ongoing
activity chips if there are multiple activities present. It does this
by:

1) Adding a second ongoing_activity_chip to status_bar.xml
2) Adding a new flow to OngoingActivityChipsViewModel that emits the *2*
   chips that should be shown, instead of just 1
3) Updating CollapsedStatusBarViewBinder to bind each chip separately
4) Updating CollapsedStatusBarFragment to show/hide each chip.

Notably: If the primary chip gets demoted to the secondary chip, then
the *data* moves from the primary view to the secondary view. The chip
views themselves *never* move. This is much cleaner from an
implementation standpoint, but it means that there is no transition
animation.

Still to come:
- Don't show the secondary chip at all if there isn't enough room
- Some amount of animation?

Bug: 364653005
Flag: com.android.systemui.status_bar_ron_chips
Test: With ron flag off, verify the single chip model still works as
expected in all cases (prioritizes the right one, swaps appropriately,
etc.)
Test: With the ron flag on, trigger multiple chips at once (e.g. be on
a phone call then start a screen recording) -> verify both chips show
with their specific data, verify tapping works as expected
Change-Id: Iaebcfce3d823760cfbf70b0a10eeea1823b193f8

Change-Id: Iefbffe0e1334f41d2990bd1144914862a2d1a69c