fix typo in subpixel-utils
Change polygon test refs to use writing modes

This requires more ref files; however, failures were seen with these
tests in Blink when the refs did not use the same writing mode as the
test itself.
Add test for stacked floats with shape-outside
First shape-margin tests.
Add Adobe as an author for these tests.
Merging https://github.com/w3c/csswg-test/pull/66