Currently the logic to check if a FCV transition is valid and update the FCV document with the correct version is pretty complex, mainly because:

• The definition of valid FCV transitions includes transitional FCV.
• It is not simple to see how updateFeatureCompatibilityVersion document will get updated: Each call (1, 2, 3) takes different arguments and the new version still has to be computed inside based on those.

For Symmetric FCV, we need to change the handling of the FCV document so we should simplify it to resolve "what FCV transition has to be done" at the beginning of setFCV and then the rest of the logic in setFCV can be more straightforward.