This should eventually have the same meaning as it does for the modules
language under the ephemeral_values language experiment, but as of this
commit is just accepted during decoding and then ignored. The rest of the
functionality will follow in subsequent commits.
There's no specific experiment guard in this case because the stack
configuration language is already experimental as a whole anyway.
This is a first pass for decoding the new stack configuration language,
which is overall pretty similar to the Terraform module language but does
have some intentional differences both in its top-level concepts -- has
embedded stacks and components instead of nested modules and resources --
and in its details, where we're making use of some learnings about where
folks have struggled with the Terraform module language.
This initial implementation should be enough for us to experiment with but
we'll probably iterate on this more in later commits as we learn from
implementing a language runtime for this and from actually trying to use
the language for real use-cases.
