R1:c3c55d82ae9d

Make "renderer", "engine", and "encoding" sticky across reloads in Differential and Diffusion

Summary:
Ref T13455. Update the other "view state" properties to work like "highlight" now works.

Some complexity here arises from these concerns:

- In "View Standalone", we render the changeset inline. This is useful for debugging/development, and desirable to retain.
- In all other cases, we render the changeset with AJAX.

So the client needs to be able to learn about the "state" properties of the…