(#17434) Support recursive interpolation

The original code for interpolation had, hidden somewhere in its depths,
supported recursive expansion of interpolations. This adds that support
back in.
(#17434) Detect loops in recursive lookup

The recursive lookup functionality was vulnerable to infinite recursion
when the values ended up referring to each other. This keeps track of
the names that have been seen in order to stop a loop from occuring. The
behavior for this was extracted to a class so that it didn't clutter the
logic of variable interpolation. The extracted class also specifically
pushes and pops on an internal array in order to limit the amount of
garbage created during these operations. This modification should be
safe so long a new Hiera::RecursiveLookup is used for every parse that
is done and it doesn't get shared in any manner.