Combine clipping rect iOS scenario test goldens to reduce maintenance burden keeping them updated

[jmagman]

The iOS scenario screenshots are a maintenance burden (see their update instruction) to keep updated, and are checked into the engine repo. I'm hitting this pain now turning on more tests for impeller, but they also have to be updated every time we do a major iOS update.

flutter/engine#54820 created 12 new clipping test golden screenshots. Can the new multiclip goldens be removed, and instead added as a new shape to the existing clip screenshots? For example, the new shape is right under the old shape? For example, this screenshot is testing multiple images at the same time:

cc @hellohuanlin

[hellohuanlin]

I think it's doable. Thought in that case we would be testing 2 things in one test. I'd like to look into more details on the overhead (is it performance?)

On the other extreme end, We could even squeeze everything in one screenshot. That'd be very hard to determine the failure.

[hellohuanlin]

We can probably remove the "large" version (I don't see how the size of the platform view matters)

• platform_view_large_cliprrect
• platform_view_large_cliprrect_multiple_clips
• platform_view_large_cliprrect_with_transform
• platform_view_large_cliprrect_with_transform_multiple_clips