So far we've only ever needed to re-parse address strings that happen not
to contain instance keys and so we've gotten away with our serialization
of these not being quite right, but given how liberally we've expected to
be able to use address strings from this package for wire format
interchange it seems likely that this is going to surprise us eventually.
Now we'll use an escaping scheme compatible with HCL's parser rather
than Go's parser, and so we can safely rely on hclsyntax.ParseTraversal
as part of reversing this operation to transform an address string back
into an address equivalent to the value it was created from.
