R1:3c0da8161967

When the Differential filetree is toggled, resize the keyboard reticle properly

Summary:
Ref T9270. Ref T12634. Emit a resize event after toggling the filetree so that things can recalculate layout.

This just does the keyboard reticle, not the mouse/edit reticle.

Test Plan:
- Used "n" to select a block.
- Used "f" to toggle the filetree.
- Saw reticle resize properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12634, T9270

Differential Revision: https://secure.phabricator.com/D17902