Improve Arcanist symbol name linter

Summary:

• Move name helper functions to ArcanistXHPASTLintNamingHook to make it easier

to write custom linters.

• Add test coverage for name functions.
• Add 'variable' and 'global' naming convention tests.
• Expand test cases.
• Improve lint message error when an unexpected message is raised during a

test.

• Remove a defunct XHP lint message.

Test Plan:

• Ran unit tests.
• Ran "arc lint --lintall" on arcanist/.

Reviewers: btrahan, nh, jungejason

Reviewed By: btrahan

CC: johnduhart, aran, epriestley, arudolph

Differential Revision: https://secure.phabricator.com/D1506