Reject nonminmal representations of UTF8 at the beginning of the 3-byte BMP range
Summary: Ref T1191. These byte ranges (\xE0\x80\x80 through \xE0\x9F\xBF) are alternate representations of characters with a different preferred minimal representation. MySQL and mbstring both reject them, and we should too.
Test Plan: Ran unit tests.
Reviewers: btrahan, arice
Reviewed By: arice
CC: chad, arice, aran
Maniphest Tasks: T1191
Differential Revision: https://secure.phabricator.com/D8313