Helper method for max text field length and validate alias length

Summary: Ref T8992, Validate alias text field length.

Test Plan: Create Phurl with alias of more than 64 characters. Get error. Reduce length of alias to successfully save Phurl.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T8992

Differential Revision: https://secure.phabricator.com/D14403