Update all instances of the progress indicator to rounded caps

Previously, we only had rounded caps for the app list and shelf apps
progress indicators.  To keep consistency across surfaces, make the
round caps as the default strategy to paint the progress indicator.

Additionally, modify the painting algorithm to adapt to the rounded caps:

- For drawing the arc during the pending animation, if start < end,
  instead of drawing two paths created by CreatePathSegment(), generate
  both paths separately and join them, so only one path is drawn and the
  intersection is accounted as part of the path.

- For drawing at 0 progress, skip creating a path in CreatePathSegment()
  if start == end to make sure that nothing is drawn, since the rounded
  caps may be drawn at a zero-length segment.

See bug for screen recording of the result.

Bug: b:311460259
Change-Id: I2f200d31c6fa0f462f6f85c5c77bfae2f3231f94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5064110
Reviewed-by: David Black <dmblack@google.com>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Commit-Queue: Ana Salazar <anasalazar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1230100}