Use Plugins DSL in Kotlin Gradle scripts

When plugins DSL is used, there is no need to
manually generate typesafe accessors for extensions and
conventions (by running `./gradlew kotlinDslAccessorsSnapshot`).

prepare/formatter/build.gradle.kts

@@ -1,7 +1,9 @@
 
 description = "Kotlin Formatter"
 
-apply { plugin("java") }
+plugins {
+    java
+}
 
 runtimeJar {
     archiveName = "kotlin-formatter.jar"