Matan Lurey 70b18ec727 Write dart:ui golden-file tests testing FilterQuality.* (flutter/engine#52687)
Work towards https://github.com/flutter/flutter/issues/147259.

Most of this is just me understanding how `FilterQuality.*` feeds into the rest of the engine, and updating our testing documentation so we all understand how to re-run these tests in the future. Here is an example output of both Impeller and non-Impeller output of `image_filter_test`:

<img width="485" alt="Screenshot 2024-05-08 at 2 25 53 PM" src="https://github.com/flutter/engine/assets/168174/58e6a4f5-98e2-4b9e-b181-4ff613ad4d29">
2024-05-10 22:15:23 +00:00
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