R1:856bdaf77e8f

Add an "Onto Branch" selector control to "Land Revision" dialog

Summary:
Ref T9952. This adds a typeahead so you can pick a branch to target.

It does not choose a default branch, the user must pick a branch explicitly.

Test Plan:
- Landed rGITTESTd587fada48fc to `master` (by typing "master").
- Landed rGITTEST86c339b2ef01 to `notmaster` (by typing "notmaster").

{F1020531}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9952

Differential Revision: https://secure.phabricator.com/D14733