KPM: In Native variants, expose the implementation dependencies as API

This simulates the behavior of the stable plugin which also exposes the
implementation dependencies in the Native targets.

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinGradleFragmentConfigurationDefinition.kt

@@ -47,6 +47,9 @@ operator fun <T : KotlinGradleFragment> KotlinGradleFragmentConfigurationDefinit
 operator fun <T : KotlinGradleFragment> KotlinGradleFragmentConfigurationDefinition<T>.plus(other: FragmentArtifacts<T>):
         KotlinGradleFragmentConfigurationDefinition<T> = copy(artifacts = artifacts + other)
 
+operator fun <T : KotlinGradleFragment> KotlinGradleFragmentConfigurationDefinition<T>.plus(other: FragmentConfigurationRelation):
+        KotlinGradleFragmentConfigurationDefinition<T> = copy(relations = relations + other)
+
 @AdvancedExternalVariantApi
 operator fun <T : KotlinGradleFragment> KotlinGradleFragmentConfigurationDefinition<T>.plus(other: FragmentCapabilities<T>):
         KotlinGradleFragmentConfigurationDefinition<T> = copy(capabilities = capabilities + other)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinGradleFragmentConfigurationRelation.kt

@@ -8,6 +8,7 @@
 package org.jetbrains.kotlin.gradle.plugin.mpp.pm20
 
 import org.gradle.api.artifacts.Configuration
+import org.gradle.api.artifacts.ConfigurationPublications
 import org.jetbrains.kotlin.gradle.utils.addExtendsFromRelation
 
 /* Internal abbreviation */
@@ -21,6 +22,33 @@ interface KotlinGradleFragmentConfigurationRelation {
     }
 }
 
+operator fun FragmentConfigurationRelation.plus(other: FragmentConfigurationRelation): FragmentConfigurationRelation {
+    if (this === KotlinGradleFragmentConfigurationRelation.None) return other
+    if (other === KotlinGradleFragmentConfigurationRelation.None) return this
+
+    if (this is CompositeFragmentConfigurationRelation && other is CompositeFragmentConfigurationRelation) {
+        return CompositeFragmentConfigurationRelation(this.children + other.children)
+    }
+
+    if (this is CompositeFragmentConfigurationRelation) {
+        return CompositeFragmentConfigurationRelation(this.children + other)
+    }
+
+    if (other is CompositeFragmentConfigurationRelation) {
+        return CompositeFragmentConfigurationRelation(listOf(this) + other.children)
+    }
+
+    return CompositeFragmentConfigurationRelation(listOf(this, other))
+}
+
+internal class CompositeFragmentConfigurationRelation(val children: List<FragmentConfigurationRelation>) :
+    FragmentConfigurationRelation {
+
+    override fun setExtendsFrom(configuration: Configuration, context: KotlinGradleFragmentConfigurationContext) {
+        children.forEach { child -> child.setExtendsFrom(configuration, context) }
+    }
+}
+
 class KotlinGradleFragmentConfigurationRelationContext internal constructor(
     val configuration: Configuration,
     context: KotlinGradleFragmentConfigurationContext

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinNativeVariantFactory.kt

@@ -26,7 +26,9 @@ data class KotlinNativeVariantConfig<T : KotlinNativeVariantInternal>(
         DefaultKotlinCompileDependenciesDefinition + KotlinFragmentKonanTargetAttribute,
 
     val apiElements: ConfigurationDefinition<T> =
-        DefaultKotlinApiElementsDefinition + KotlinFragmentKonanTargetAttribute,
+        DefaultKotlinApiElementsDefinition
+                + KotlinFragmentKonanTargetAttribute
+                + FragmentConfigurationRelation { extendsFrom(dependencies.transitiveImplementationConfiguration) },
 
     val hostSpecificMetadataElements: ConfigurationDefinition<T> =
         DefaultKotlinHostSpecificMetadataElementsDefinition,