(#22288) Add post_compile_hook to Puppet::Parameter

Without this commit there is no message sent to parameters (and
subclasses thereof) to indicate the catalog has completed compilation.
This is an issue for any parameter that is not based on
Puppet::Type::RelationshipMetaparam and needs to do something on
completion of catalog compilation. An example for such application would
be verifying some other resource made it into the catalog so that a
value may be used fro it for the current type.

This commit add an enhancement to the Puppet::Type#finish method. This
method will now list through all parameters, including
Puppet::Type::RelationshipMetaparam parameters, and call the
post_compile_hook method if implemented. This commit also adds an
abstract method comment to Puppet::Parameter.