[ios] Implement PageControl in BubbleView

Implements a page control using a UIStackView and the same
circlebadge.fill used by the UIKit UIPageControl. UIPageControl could
not be used because of the excessive horizontal padding.

BubblePageControlPage is passed through the BubbleView logic to indicate
which page should be highlighted.

Video: https://screencast.googleplex.com/cast/NTU5OTc1NDAwNzM0NzIwMHxlNTk1NDJlMS05ZA

Bug: 413461470
Change-Id: Ib35a9e5f3f5308b639a2c1415b7bcc65d5ab9a8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6576940
Commit-Queue: Chris Lu <thegreenfrog@google.com>
Reviewed-by: Ginny Huang <ginnyhuang@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Auto-Submit: Chris Lu <thegreenfrog@google.com>
Cr-Commit-Position: refs/heads/main@{#1464300}