Based on feedback during earlier alpha releases, we've decided to move
forward with the current design for the first phase of config-driven
refactoring.
Therefore here we've marked the experiment as concluded with no changes
to the most recent incarnation of the functionality. The other changes
here are all just updating test fixtures to no longer declare that they
are using experimental features.
Configuration-driven moves are represented in the plan file by setting
the resource's `PrevRunAddr` to a different value than its `Addr`. For
JSON plan output, we here add a new field to resource changes,
`previous_address`, which is present and non-empty only if the resource
is planned to be moved.
Like the CLI UI, refresh-only plans will include move-only changes in
the resource drift JSON output. In normal plan mode, these are elided to
avoid redundancy with planned changes.
