Allow dialogs to opt in to being resizable

Summary: Ref T11034. Ref T4788. This allows you to resize the typeahead browse dialog if you want. I plan to let you resize the object selector dialog in the future.

Test Plan: {F1695433}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4788, T11034

Differential Revision: https://secure.phabricator.com/D16156