(#4655) Allow stage to be set using a default class parameter

For example:

stage{ pre: before => Stage[main] }
class someclass ($stage=pre ) { ... }
class { someclass: }

This transplants adding the edge from the resource to the stage from
the compiler into when the resource is evaluated. This moves adding
the stage edges to after when the defaults are copied into the
resources, making them available.

Paired-with: Jesse Wolfe <jesse@puppetlabs.com>