Update DisplayList method names for Flutter style guidelines

[flar]

As indicated in flutter/engine#28656 the comments made a number of suggestions for how to make the DisplayList API better follow our C++ code style guidelines.

[flar]

Also consider setCaps, setJoins and setAA should have better names (regardless of capitalization style).

Also consider renaming "transparentOccluder" as the name contradicts itself ("hides something with a thing that doesn't hide anything").

[flar]

Should have been closed by flutter/engine#28753

[github-actions]

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