[Gradle][MPP] Mark KotlinTargetsContainer and KotlinTargetHierarchyBuilder with KotlinTargetsDsl annotation

To prevent confusing shortcuts defined on `KotlinTargetsContainer`
when declaring a KotlinTargetHierarchy:

e.g.

```kotlin
kotlin {
    targetHierarchy.default {
        common {
            ios() // <- [DSL_SCOPE_VIOLATION]
            //'fun ios(): Unit' can't be called in this context
            // by implicit receiver. Use the explicit one if necessary
        }
    }
 }
```

^KT-53570 Verification Pending

libraries/tools/binary-compatibility-validator/reference-public-api/kotlin-gradle-plugin-api.txt

@@ -1121,6 +1121,9 @@ public abstract interface class org/jetbrains/kotlin/gradle/plugin/KotlinTargets
 	public abstract fun getPresets ()Lorg/gradle/api/NamedDomainObjectCollection;
 }
 
+public abstract interface annotation class org/jetbrains/kotlin/gradle/plugin/KotlinTargetsDsl : java/lang/annotation/Annotation {
+}
+
 public abstract interface class org/jetbrains/kotlin/gradle/plugin/KotlinTestRun : org/jetbrains/kotlin/gradle/plugin/KotlinExecution {
 	public abstract fun filter (Lgroovy/lang/Closure;)V
 	public abstract fun filter (Lkotlin/jvm/functions/Function1;)V