Gradle, native: Add a DSL shortcut for iOS, watchsOS and tvOS

This patch adds a group of shortcut DSL methods allowing a user to
create simulator and device targets for Apple platforms along with
corresponding common source set(s) in one command. iOS, tvOS and
watchOS targets are supported.

Issue #KT-33856 fixed

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

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.gradle.plugin
 
 import org.gradle.api.NamedDomainObjectCollection
+import org.gradle.api.NamedDomainObjectContainer
 
 interface KotlinTargetsContainer {
     val targets: NamedDomainObjectCollection<KotlinTarget>
@@ -13,4 +14,8 @@ interface KotlinTargetsContainer {
 
 interface KotlinTargetsContainerWithPresets : KotlinTargetsContainer {
     val presets: NamedDomainObjectCollection<KotlinTargetPreset<*>>
+}
+
+interface KotlinSourceSetContainer {
+    val sourceSets: NamedDomainObjectContainer<KotlinSourceSet>
 }