[TTS] Refactor: java ResolvedSearchTerm immutable.

Adds an encapsulation of the server response into a new immutable
java class: ResolvedSearchTerm.  We have a native encapsulation of
this but nothing on the Java side.  It would be even better to
have the Java and native classes linked, but I'm not sure how to
do that or if it's worth it.

Bug=942663

Change-Id: I6492b63f7b74787d493b2c2aee2db59129881cd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1526402
Commit-Queue: Donn Denman <donnd@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Auto-Submit: Donn Denman <donnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641796}
6 files changed