Investigate kapt optimizations

[restingbull]

Avenues:

• Avoid running kapt over the entire classpath
• Generate stubs and use light analysis to move kapt into a parallel action

Correctness considerations:

• kapt currently generates files for the entire classpath.

[jongerrish]

Update: Kapt now runs in a separate action for the new flow, mnemonic = KotlinKapt