Previously we would attempt to DynamicExpand during the validate walk and
then validate each expanded instance separately. However, this meant that
we would not be able to validate the contents of a block where count = 0
or if count is not yet known.
Here we instead do a more static validation pass against the resource
configuration itself, setting count.index to cty.UnknownVal(cty.Number) so
we can type-check everything inside the block as being correct regardless
of the final count.
This is another step towards repairing the "validate" command for our
changed assumptions in a world where we have a more sophisticated type
checker.
This doesn't yet address the remaining problem that the expression
evaluator can't, with the current state structures, distinguish between
a completed resource with count = 0 and a resource that doesn't exist
at all (during validate), and so we'll still get errors if an expression
elsewhere in configuration refers to a dynamic index of a resource with
"count" set. That's a pre-existing condition that's no longer being masked
by _this_ problem, but can't be addressed until we've introduced the new
state types (states.State, etc) and thus we _can_ distinguish these two
situations. That will therefore be addressed in a later commit.
cf4a5e6336