Correctly focus elements in Workflow dialogs

Summary:
JX.Workflow does a JX.DOM.find() for the sigil default, but fails because we
render with phutil_render_tag() instead of javelin_render_tag() so sigils are
not converted correctly.

Test Plan:
Opened an inline comment in differential, got focus on the <textarea />

Reviewed By: tuomaspelkonen
Reviewers: tuomaspelkonen
CC: aran, tuomaspelkonen, epriestley
Differential Revision: 259