[AGP] Register generated kotlin sources with java source set

[hfmehmed]

Intially we registered java output folder with java sourceset and kotlin output folder with kotlin sourceset. Two reasons for this:

1. It seemed like the right way to model things
2. We could only register one directory with one sourcset (registering kotlin output with java sourcset would override the previous registration)

Number 2 is fixed in AGP 9.0.0-alpha14.

However, it turns out number 1 is problematic. Registering with kotlin sourceset ends up in a circular task dependency with built in kotlin feature enabled.

At the moment, we avoid the circular exception because we look at all the task dependencies of the kotlin sourceset and exclude the ksp task. But this is a project isolation breaking logic which we need to remove at some point.

The flow looks like the following more or less:
KSP task -> register kotlin output with kotlin.sources -> kotlin.sources flows into kotlinCompilation.defaultSourceSet.kotlin.srcDirs() this happens in AGP built in kotlin -> kotlin.srcDirs() is an input to ksp task leading to the circularlity.