Provide a DSL for publication settings (#1869)

* Provide a DSL for publication settings
* Rename DSL method publication -> mavenPublication
* Fix gradle task input/output validation

 #KT-26771 fixed.

libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinTarget.kt

@@ -5,12 +5,15 @@
 
 package org.jetbrains.kotlin.gradle.plugin
 
+import groovy.lang.Closure
+import org.gradle.api.Action
 import org.gradle.api.Named
 import org.gradle.api.NamedDomainObjectContainer
 import org.gradle.api.Project
 import org.gradle.api.attributes.HasAttributes
 import org.gradle.api.component.SoftwareComponent
 import org.gradle.api.internal.component.UsageContext
+import org.gradle.api.publish.maven.MavenPublication
 
 interface KotlinTargetComponent : SoftwareComponent {
     val target: KotlinTarget
@@ -39,5 +42,8 @@ interface KotlinTarget: Named, HasAttributes {
 
     fun createUsageContexts(): Set<UsageContext>
 
+    fun mavenPublication(action: Closure<Unit>)
+    fun mavenPublication(action: Action<MavenPublication>)
+
     override fun getName(): String = targetName
 }