Make PropertyMetadataImpl a data class

To allow property delegates to use property metadata as a key in the hash map,
and to improve debugging experience

core/builtins/src/kotlin/PropertyMetadata.kt

@@ -29,4 +29,6 @@ public interface PropertyMetadata {
 /**
  * @suppress
  */
-public class PropertyMetadataImpl(override val name: String): PropertyMetadata
+public data class PropertyMetadataImpl(override val name: String): PropertyMetadata {
+    override fun toString() = "PropertyMetadata(name=$name)"
+}