Move SkFrontBufferedStream into Android-only dir

Bug: skia:10154

Add client_utils for code that is specifically for a single client.
Move SkFrontBufferedStream into its android/ subdir. Rename the class
to android::skia::FrontBufferedStream. Temporarily leave in
SkFrontBufferedStream until Android updates to the new API.

Add a new optional target for client_utils/android. It is built in dev
builds for testing, and when building for the Android framework.

Change-Id: Ie0f425051ea370aab7861d61150a3d6007214a93
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/284721
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
12 files changed