Add test for the clear attribute presentational hints on BR elements

[Psychpsyo]

This tests that these presentational hints from the spec are honored:

br[clear=left i] { clear: left; }
br[clear=right i] { clear: right; }
br[clear=all i], br[clear=both i] { clear: both; }

Written as part of the Ladybird project, should pass in all browsers.
Also, bonus example page where this behavior is used: https://archive.org/details/mspaint_xp_version