Center-align bubble row

Center aligned bubbles change x position based on shown bubble count.
Update animations to reflect new behavior.

-On bubble add/remove
---Update pointer position
---Update all bubble positions

-New bubble x computation
---row left = screen center - half row width
---bubble left = row left + bubble index * space

Bug: 131849856
Test: manual
Change-Id: I9294c6831a648b01d16eef389e951585fd2fbde9