Run build-logic Kotlin compilation out of process on CI

[3flex]

Kotlin uses a compilation daemon by default. This is the fastest execution mode and usually preferred, because the Kotlin compilation environment can be setup once and reused.

However, it leaves the compilation daemon running for the lifetime of the Gradle daemon. Again, usually what we want, but in the case of the build-logic project which depends on kotlin-dsl, it will launch a Kotlin 1.6.21 daemon (matching Gradle's embedded Kotlin version) if the build-logic:compileKotlin task has to run, which cannot be reused by other compilation tasks (which use Kotlin 1.7.10). The 1.6.21 compilation daemon then remains in memory, unused.

This PR changes the compilation strategy to be out of process when running on CI. This means the 1.6.21 compilation environment is terminated as soon as the build-logic:compileKotlin task completes, which will free that memory for the remainder of the build.

I actually think this is a good trade off for all builds, not just on CI, but happy to hear thoughts on this.

[3flex]

Also note that this is an @Internal property so changes in its value are not considered for up to date checks or build caching - having a different setting for CI will not affect remote cache hits.