Render the clone URI input field as readonly.
There's no particular reason to allow the user to edit the clone URI field in Diffusion; editing it has no meaning and if you fat finger the keyboard, it's quite possible that the user will either accidentally clear and/or modify the URI before copying (bit me this morning).
Adding a readonly attribute to the input field allows the same benefit (URI is easily selectable) while preventing such accidental input. Fixes T4246.
Test Plan: Verified that the desired behavior is present in both Chrome, Safari, and Firefox. Field remains selectable with one click, but field is not editable.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley
CC: Korvin, epriestley, aran
Maniphest Tasks: T4246
Differential Revision: https://secure.phabricator.com/D7810