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