Support Kotlin nullability

- Kotlin rendering will always show nullability information. If a type isn't annotated, we don't change anything (meaning with don't add a `!`)
- Java rendering will have annotations if the Java sources had them and if the Kotlin sources are null. We currently don't inject fake @NonNull annotations because I felt that would be too noisy.

Fixes: 165139177
Change-Id: I0ca306367db661ce4f073f008f27bee315b10ac4
74 files changed