Use `.dicts_suggest` in `po.R` and `ppl.R`

[advieser]

Closes https://github.com/mlr-org/mlr3pipelines/issues/717

Main work was done in misc: https://github.com/mlr-org/mlr3misc/pull/120. See there for details.

Now waiting for next CRAN release of mlr3misc. TODO before merging: Check that the version number for mlr3misc in DESCRIPTION is correct (depending on whether the next release is minor or patch).