Offline Dictation: A11y quick settings improvements for SODA downloads

This change modifies the behavior of the a11y quick settings when
notifying the user of SODA download changes. Specifically, we ensure
that the Dictation locale is considered before notifying the user.

For successful downloads, we only notify the user if both the SODA
binary and the language pack matching the Dictation locale have been
installed.

For progress, we only notify the user when the language pack matching
the Dictation locale updates its progress.

For errors, we notify the user if either the SODA binary or the
language pack matching the Dictation locale encounters an error; we
do not notify the user if an irrelevant language pack fails.

This change models https://crrev.com/c/3082314, which implements
very similar logic.

Bug: 1173135
Change-Id: I8ed5674dc0e1ebdab479fcd08df353ab06a45808
AX-Relnotes: N/A
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3086421
Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Reviewed-by: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#911752}