Make the function work specifically how we need for RequiresReplace.
Skip index changes, any set changes are only recorded as the set itself,
and filter out duplicate paths.
Add a few more tests to check for various nested structures.
Rather than try and make a generalized path function here, what we
really need in a function to generate the paths needed for
RequiresReplace. This needs to take into account that sets elements
don't need to be indexed themselves, and changes to collection index
values aren't needed.
PathFromFlatmapKey is used to convert a flatmap key to a cty.Path, and
ensures it conforms to the type schema.
This is used when handling Diffs, where the ResourceAttrDiffs are
indexed by the flatmapped key values, and we need to convert those to
addresses to apply to a cty.Value.
James Bardin