Diagnostics: Enable fake providers for live app.

Remove all direct references to mojo-lite and redirect through
diagnostics_types.

Add internal useFakeProviders flag to mojo_interface_provider that can
switch between real and fake providers at application start.

Change-Id: Iea6c1e73951125115a8c53e200d681caf1ce40e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2893826
Commit-Queue: Gavin Dodd <gavindodd@google.com>
Reviewed-by: Joon Ahn <joonbug@chromium.org>
Cr-Commit-Position: refs/heads/master@{#883622}