RELAND: ShapeDetection: add support for Text Detection in Mac

The original CL got reverted due to out-of-bots partial availability
warnings such as :
> error: 'CIRectangleFeature' is only available on macOS 10_10 or newer
(1st spotted in
This CL adds forward-declaration of this class before 10.11.

Incidentally, it's the same issue addressed in e.g.

Original issue's description:
> ShapeDetection: add support for Text Detection in Mac
> This CL adds text detection for Mac in services/shape_detection,
> and also adds unittest for it, that will be run, like the
> other specific unittests, in the mac gpu bots.
> BUG=697925
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.mac:mac_optional_gpu_tests_rel
> TEST= unittests that can be run anywhere like this:
> out/gn/service_unittests  --gtest_filter=*TextDetection* --use-gpu-in-tests
> and demo page, e.g.
> ./out/gn/  --enable-blink-features=ShapeDetection
> Review-Url:
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.mac:mac_optional_gpu_tests_rel, since it's a trivial fwd-declaration.

Cr-Commit-Position: refs/heads/master@{#454816}
12 files changed