[Kotlin] Add Kotlin source support to build chain (#37)

This adds unidirectional Kotlin support for writing code in Kotlin and using it in Groovy.

Extracted from #29

build.gradle.kts

@@ -3,6 +3,8 @@ import com.gradle.publish.PublishTask.GRADLE_PUBLISH_SECRET
 
 plugins {
   id("groovy")
+  id("org.jetbrains.kotlin.jvm") version "1.8.20"
+  id("io.gitlab.arturbosch.detekt") version "1.22.0"
   id("com.gradle.plugin-publish") version "1.2.0"
   id("java-gradle-plugin")
 }
@@ -68,3 +70,24 @@ dependencies {
   testImplementation("junit:junit:4.13.2")
 }
 
+tasks.compileGroovy {
+  classpath += files(tasks.compileKotlin.flatMap { it.destinationDirectory })
+}
+
+tasks.classes {
+  dependsOn(tasks.compileGroovy)
+}
+
+detekt {
+  parallel = true
+  autoCorrect = true
+
+  buildUponDefaultConfig = true // preconfigure defaults
+  config = files("$rootDir/config/detekt-config.yml")
+
+  allRules = false // activate all available (even unstable) rules.
+}
+
+dependencies {
+  detektPlugins("io.gitlab.arturbosch.detekt:detekt-formatting:1.22.0")
+}

config/detekt-config.yml

@@ -0,0 +1,20 @@
+formatting:
+  active: true
+  Indentation:
+    active: true
+    indentSize: 2
+  PackageName:
+    active: false
+
+style:
+  active: true
+  ReturnCount:
+    max: 4
+
+complexity:
+  LongMethod:
+    excludes: [ '**/test/**', '**/androidTest/**', '**/commonTest/**', '**/jvmTest/**', '**/jsTest/**', '**/iosTest/**' ]
+
+naming:
+  PackageNaming:
+    packagePattern: '[a-z]+(\.[a-z][A-Za-z0-9_]*)*'