Add a linter rule for uppercase constant definitions

Summary: Ref T7409. Adds a linter rule to ensure that constant are defined as being uppercase. Based on Generic_Sniffs_NamingConventions_UpperCaseConstantNameSniff.

Test Plan: Added test cases.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7409

Differential Revision: https://secure.phabricator.com/D12366