Because we handle FixUpBlockAttrs after dynamic block expansion, when
resolving variables we unfortunately need to consider the possibility of
both dynamic block expansion _and_ the block attrs fixup.
To accommodate this we have a variant of dynblock.VariablesHCLDec that
instead walks using the configschema.Block representation of the schema
and applies the same opportunistic schema rewrite used by FixUpBlockAttrs
at each body encountered during the walk.
Martin Atkins