AS always shows Duplicate content roots detected popup when Gradle sync is performed

[mars885]

At the moment of this writing, KSP requires us to specify where the generated code lives. If we were to omit it, the generated code does not get picked up and the build fails.

The solution, however, causes the popup with text "Duplicate content roots detected" appear after every Gradle sync.

Firstly, follow google/ksp#37 issue and see whether a better solution is provided.
Second, follow AS issue for Duplicate content roots detected popup appearing.