The <fill-rule> in the polygon() syntax is not handled because it doesn't
matter to shape-outside at all.
The reftests are numbered from 018 to avoid conflict with the w3c upstream
ones according to this list.
https://test.csswg.org/harness/results/css-shapes-1_dev/grouped/
Reftest 018 to 025 are under various writing-modes, 026 to 029 are testing
empty float area, 030 to 031 are testing polygon containing horizontal
lines.
MozReview-Commit-ID: FPUbMdZsvu6
