Add FakeSpeechRecognitionRecognizerClient

This CL adds a fake, do-nothing client for speech recognition because
it's used in separate repos from chromium for tests.  This allows us
to add methods to the client's mojom definition, and also default
implementations to keep the third-party tests compiling.

Change-Id: I2df3eed7454ba0866440c67bc8ef7bd4879bddc2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6580415
Commit-Queue: Frank Liberato <liberato@chromium.org>
Reviewed-by: Evan Liu <evliu@google.com>
Cr-Commit-Position: refs/heads/main@{#1464367}