What is the atomic operation in `dm_disentangle()`?

[krlmlr]

We want to split the process into "planning" and "doing", just like dm_wrap_tbl(), to be able to guess a plan if only the result of dm_disentangle() is given (e.g. got_chars nested table -> dm).

Something like: "duplicate a table and all tables that can be reached if we omit the tables we have already visited on the path"?