This "kitchen sink" commit is mainly focused on supporting "targets" as
a new sub-category of addresses, for use-case like the -target CLI option,
but also includes some other functionality to get closer to replacing
terraform.ResourceAddress and fill out some missing parts for representing
various other address types that are currently represented as strings
in the "terraform" package.
This is for parsing the type of provider configuration address we write
into state in order to remember which provider configuration is
responsible for each resource.
Martin Atkins