R1:b2890eeb0e6f

Add "final" to all Phabricator "Controller" classes

Summary:
These are all unambiguously unextensible. Issues I hit:

- Maniphest Change/Diff controllers, just consolidated them.
- Some search controllers incorrectly extend from "Search" but should extend from "SearchBase". This has no runtime effects.
- D1836 introduced a closure, which we don't handle correctly (somewhat on purpose; we target PHP 5.2). See T962.

Test Plan: Ran "testEverythingImplemented" unit test to identify classes extending…