Fix almost all remaining schemata issues
Summary:
Ref T1191. This fixes nearly every remaining blocker for utf8mb4 -- primarily, overlong keys.
Remaining issue is https://secure.phabricator.com/T1191#77467
Test Plan: I'll annotate inline.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley, hach-que
Maniphest Tasks: T6099, T6129, T6133, T6134, T6150, T6148, T6147, T6146, T6105, T1191
Differential Revision: https://secure.phabricator.com/D10601