Add missing alias annotations (#5561)

core/interfaces/i_registrable_field.js

@@ -28,6 +28,7 @@ const Field = goog.requireType('Blockly.Field');
  * @typedef {{
  *     fromJson:IRegistrableField.fromJson
  * }}
+ * @alias Blockly.IRegistrableField
  */
 let IRegistrableField = {};
 

core/positionable_helpers.js

@@ -57,6 +57,7 @@ exports.horizontalPosition = horizontalPosition;
  *   horizontal: !horizontalPosition,
  *   vertical: !verticalPosition
  * }}
+ * @alias Blockly.uiPosition.Position
  * @package
  */
 let Position;