We cannot create kapt configurations in `KotlinGradleSubplugin.apply`,
because `apply` is invoked after a script is evaluated, so user cannot
refer to kapt configurations in script.
We cannot call `apply` before script's evaluation, because
then we might not be able to determine
if a Gradle plugin corresponding to a subplugin is appled.
For example in case of the following script:
```
apply plugin: "kotlin"
apply plugin: "kotlin-kapt"
```
subplugin's apply will exit early because Gradle plugin "kotlin-kapt"
is not applied yet, when "kotlin"'s apply is evaluated.
Alexey Tsvetkov
cb549cba00