Require ClassMatchesFilename sniff to pass for most of tests/

Require ClassMatchesFilename sniff to pass for most of tests/

phpunit-patch-coverage assumes that the filename matches the classname
as a performance optimization. And for most test cases, this is true. We
should enforce this with PHPCS, mostly to help developers not make
mistakes.

Test cases that have mock classes will need to ensure that the test case
class that matches the filename comes first, since that's the only class
the sniff will look at.

Tests in GlobalFunctions/ and maintenance/ are still exempted for now,
since they don't match yet.

Change-Id: Iede341504290f5ba2da1c81908069ba9d465600f