Use separate configuration for resolving native compiler plugin artifacts

Kotlin/JVM and Kotlin/JS use shaded compiler, but
Kotlin/Native uses non-shaded one.
Serialization plugin was configured to use either shaded or non-shaded
plugin version, because we used one configuration for resolving
compiler plugins.
This change introduces 'kotlinNativeCompilerPluginClasspath' configuration
for resolving Kotlin/Native compiler plugins.

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

@@ -67,6 +67,7 @@ interface KotlinGradleSubplugin<in KotlinCompile : AbstractCompile> {
     fun getCompilerPluginId(): String
 
     fun getPluginArtifact(): SubpluginArtifact
+    fun getNativeCompilerPluginArtifact(): SubpluginArtifact? = null
 }
 
 open class SubpluginArtifact(val groupId: String, val artifactId: String, val version: String? = null)