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`).

libraries/examples/annotation-processor-example/build.gradle.kts

@@ -1,8 +1,8 @@
 description = "Simple Annotation Processor for testing kapt"
 
-apply {
-    plugin("kotlin")
-    plugin("maven") // only used for installing to mavenLocal()
+plugins {
+    kotlin("jvm")
+    maven // only used for installing to mavenLocal()
 }
 
 dependencies {