Reland "[Read Aloud] Fix scrolling behavior"

This is a reland of commit b131e478a844a7d0a1ba55c48517199be3ec80f7

This was reverted in an attempt to fix a failing bot but it wasn't the
real culprit, so relanding. See comment on original CL.

Original change's description:
> [Read Aloud] Fix scrolling behavior
>
> Previously:
>   - We were scrolling on every highlight so if there were multiple
>     highlights in one granularity, the bottom of the granularity would
>     get centered. This would cause issues when the font size is large.
> Now:
>   - Scroll the first of the current highlights instead of the last
>   - If the full highlight is longer than half the page, then scroll the
>     highlight to the top so more of the highlight is in view
>   - Otherwise if part of the highlight is cut off but not longer than
>     half the height, scroll the first highlight to the center.
>
> Fixed: 343516220, 343224952
> Change-Id: I31f9a5c8f167040555e980085961ebc959f03cce
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5582106
> Commit-Queue: Kristi Saney <kristislee@google.com>
> Auto-Submit: Kristi Saney <kristislee@google.com>
> Reviewed-by: Eitan Goldberger <eitang@google.com>
> Cr-Commit-Position: refs/heads/main@{#1308194}

Change-Id: I29bedb755b3e69f74e9f969fa96bc0b44b039972
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5588474
Commit-Queue: Kristi Saney <kristislee@google.com>
Reviewed-by: Eitan Goldberger <eitang@google.com>
Cr-Commit-Position: refs/heads/main@{#1308760}