[Gradle] Add withSourcesJar to gradle dsl

* Each target can be configured to either publish or not its sources.
* For convenience withSourcesJar available also on kotlin multiplatform
  extension level. It then calls `withSourcesJar` for each target.

^KT-55881 In Progress

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

@@ -38,6 +38,8 @@ interface KotlinTarget : Named, HasAttributes {
 
     val publishable: Boolean
 
+    fun withSourcesJar(publish: Boolean = true)
+
     val components: Set<SoftwareComponent>
 
     fun mavenPublication(action: MavenPublication.() -> Unit) = mavenPublication(Action { action(it) })

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinMultiplatformExtension.kt

@@ -65,6 +65,10 @@ abstract class KotlinMultiplatformExtension(project: Project) :
 
     fun metadata(configure: Action<KotlinOnlyTarget<KotlinMetadataCompilation<*>>>) = metadata { configure.execute(this) }
 
+    fun withSourcesJar(publish: Boolean = true) {
+        targets.all { withSourcesJar(publish) }
+    }
+
     fun <T : KotlinTarget> targetFromPreset(
         preset: KotlinTargetPreset<T>,
         name: String = preset.name,

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

@@ -67,6 +67,11 @@ abstract class AbstractKotlinTarget(
     override val publishable: Boolean
         get() = true
 
+    internal var publishSources: Boolean = true
+    override fun withSourcesJar(publish: Boolean) {
+        publishSources = publish
+    }
+
     @InternalKotlinGradlePluginApi
     override val kotlinComponents: Set<KotlinTargetComponent> by lazy {
         val mainCompilation = compilations.getByName(KotlinCompilation.MAIN_COMPILATION_NAME)

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

@@ -58,6 +58,11 @@ internal class ExternalKotlinTargetImpl internal constructor(
         artifactsTaskLocator.locate(this)
     }
 
+    private var publishSources: Boolean = true
+    override fun withSourcesJar(publish: Boolean) {
+        publishSources = publish
+    }
+
     override val artifactsTaskName: String
         get() = artifactsTask.name