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`).

compiler/tests-java8/build.gradle.kts

@@ -1,7 +1,9 @@
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
-apply { plugin("kotlin") }
-apply { plugin("jps-compatible") }
+plugins {
+    kotlin("jvm")
+    id("jps-compatible")
+}
 
 dependencies {
     testCompile(projectTests(":compiler:tests-common"))