We don't currently have any need for this information, but we're
propagating it out of helper/schema here pre-emptively so that once we
later have a use for it we will not need to rebuild the providers to gain
access to it.
The long-term expected use-case for this is to have Terraform Core use
static analysis techniques to trace the path of sensitive data through
interpolations so that intermediate results can be flagged as sensitive
too, but we have a lot more work to do before such a thing would actually
be possible.
zcldec now has its own function for computing the implied type for a spec,
so we can use that instead of our own logic.
The zcldec logic is more general since its spec model is more general than
our schema model here, but it produces the same results for the subset
of specifications that our DecoderSpec method produces.
This returns a cty.Type that the caller can expect to recieve when
decoding a value using the (not yet implemented) decoder specification
for a given schema.
Rob Campbell