Improve LINT_KEYWORD_CASING linter rule

Summary: Ref T7409. Improve ArcanistXHPASTLinter::LINT_KEYWORD_CASING to include additional token types. Based on Generic_Sniffs_PHP_LowerCaseKeywordSniff.

Test Plan: arc unit

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7409

Differential Revision: https://secure.phabricator.com/D12367