No, Puppet has no such feature per se, but I don't see what advantage you hope it would provide, relative to simply declaring the contents of the class body directly at the same point.
Moreover, if you're inclined to declare a class in the same manifest in which you define it -- which runs counter to the prevailing views on good style -- I don't see how being able to merge those into a single statement would provide more than the most trivial advantage. You would save yourself literally one word of code by not repeating the class name.
John
John