There is a limitation of libreadline where no context/userdata
can be passed to completion functions. Thi affects iwctl since
the entity value isn't known to completion functions.
Workarounds such as getting the default device are employed but
its not a great solution.
Instead hack around this limitation by parsing the prompt to
extract the entity (second arg). Then use a generic match function
given to readline which can call the actual match function and
include the entity.
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