Document full impact of UseCompatibilityLevel

[clement911]

It would be great to have a doc page about the impact of using the various compatibility level on sql server with UseCompatibilityLevel.

We're considering using UseCompatibilityLevel to avoid the new Contains to OPENJSON translation. However, we can't figure out whether there will be other impacts.

[roji]

In 8.0 it's really only the Contains/OPENJSON translation. For 9.0 we'll probably introduce a better mechanism for opting out of the OPENJSON translation for this case.

Regardless, I agree that we should probably include a note on the actual effects of UseCompatibilityLevel (moving to the docs repo).