Add PHPAST test cases for most lexer patterns

Summary: Ref T4334. Adds test cases for most of the lexer rules: tags, literals, and comments. Remaining lexer rules are mostly difficult to test in isolation, or have a known issue in the case of HEREDOC.

Test Plan: The JSON dumps aren't very human readable, so I'm verifying that the parser output is sane using the web UI PHPAST tool before committing it to tests.

Reviewers: btrahan, Firehed

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4334

Differential Revision: https://secure.phabricator.com/D8026