Generating strings and comparing them to implement Equal is a quick and
easy solution. Unfortunately when this code is in the hot path, it
becomes very expensive, so this commit changes some of those instances
to compare the values directly.
Combined with using addr.Equal instead of checking for string equality,
this makes Terraform dramatically faster for some operations, such as
generating large JSON plans.
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.
Alisdair McDiarmid