Enable Vector Pass Output when Motion Blur is Enabled

In-render motion blur and the motion vector pass are not mutually exclusive in compositing. Enabling motion blur should not automatically disable the ability to output a vector pass. Which can be still useful for things like temporal de-noising, adding further motion blur in post etc.

Perhaps it's due to the implementation in Cycles itself. But ideally the user should have the option to choose to output the pass or not. Instead of being forced into a binary choice.

Currently the only option for scenes using in-render motion blur is to create a separate scene with motion blur disabled and render everything twice just to be able to render a vector pass. Which is massively inefficient.