Polish `buildSrc`
Polish `buildSrc`

Reuse `extra` from `gradleKotlinDsl()`.

gradle/gradle,gradle/gradle,robinverduijn/gradle,robinverduijn/gradle,gradle/gradle,gradle/gradle-script-kotlin,robinverduijn/gradle,gradle/gradle,gradle/gradle,blindpirate/gradle,blindpirate/gradle,blindpirate/gradle,blindpirate/gradle,robinverduijn/gradle,blindpirate/gradle,blindpirate/gradle,blindpirate/gradle,robinverduijn/gradle,blindpirate/gradle,gradle/gradle,gradle/gradle,gradle/gradle,robinverduijn/gradle,gradle/gradle-script-kotlin,gradle/gradle,robinverduijn/gradle,robinverduijn/gradle,gradle/gradle,blindpirate/gradle,robinverduijn/gradle,robinverduijn/gradle,blindpirate/gradle,robinverduijn/gradle