R1:1ee6ecf39768

Move "BoardResponseEngine" toward a more comprehensive update model

Summary:
Depends on D20639. Ref T4900. Currently, "BoardResponseEngine" has a `setObjectPHID()` method. This is called after edit operations to mean "we just edited object X, so we know it needs to be updated".

Move toward `setUpdatePHIDs(...)` in all cases, with `setUpdatePHIDs(array(the-object-we-just-edited))` as a special case of that. After this change, callers pass:

- An optional list of PHIDs they know need to be updated on the…