[Gradle] Move publishableSources flag to InternalKotlinTarget

^KT-55881 Verification Pending

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/AbstractKotlinTarget.kt

@@ -67,7 +67,7 @@ abstract class AbstractKotlinTarget(
     override val publishable: Boolean
         get() = true
 
-    internal var publishableSources: Boolean = true
+    override var publishableSources: Boolean = true
     override fun withSourcesJar(publish: Boolean) {
         publishableSources = publish
     }

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/InternalKotlinTarget.kt

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.gradle.plugin.KotlinTargetComponent
 import org.jetbrains.kotlin.tooling.core.HasMutableExtras
 
 internal interface InternalKotlinTarget : KotlinTarget, HasMutableExtras {
+    var publishableSources: Boolean
     val kotlinComponents: Set<KotlinTargetComponent>
     fun onPublicationCreated(publication: MavenPublication)
 }

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/external/ExternalKotlinTargetImpl.kt

@@ -58,9 +58,10 @@ internal class ExternalKotlinTargetImpl internal constructor(
         artifactsTaskLocator.locate(this)
     }
 
-    private var publishSources: Boolean = true
+    override var publishableSources: Boolean = true
+
     override fun withSourcesJar(publish: Boolean) {
-        publishSources = publish
+        publishableSources = publish
     }
 
     override val artifactsTaskName: String