fix($http): add support for PATCH short method

Commit 46691c2721735c27426b721d780e8816d502b9f2 removed the short method for PATCH from $http because there were too many unknowns. However, #5823 schedules PATCH to be re-added for the 1.3.x milestone.

This change adds the short method for PATCH back to the $http library, including tests.

Closes #5823