This doesn't actually work yet because the main implementation functions
are not written, but this is a sketch of the general layout of things that
the lang/eval package was designed to support: the planning phase first
lets lang/eval drive based on the desired state it discovers gradually in
the configuration, but afterwards it then does followup work for any
resource instances that didn't appear in the desired state but yet are
present in the previous round state.
This overall structure should allow the planning engine to discover all
of the changes that need to be made to resource instances without any
direct knowledge of how the OpenTofu language works and how the module
author chose to describe the desired state as code.
Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
