Move Ext.define() default values also to tag classes.

lib/jsduck/ast.rb

lib/jsduck/builtins/alias.rb

lib/jsduck/builtins/alternate_class_names.rb

lib/jsduck/builtins/extends.rb

lib/jsduck/builtins/mixins.rb

lib/jsduck/builtins/requires.rb

lib/jsduck/builtins/tag.rb

lib/jsduck/builtins/uses.rb

lib/jsduck/builtins_registry.rb