minor, extradite __trans_*() operations into {date-core,time-core,dt-core}-private.h

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, make all __trans_*() routines return the format
Revert "minor, translate named input formats in __trans_dtfmt() to their dfmt counterpart"

This reverts commit 26d7e37de4ed5329f2119e319dabb185e9bb44c4.
Merge branch 'feat/named-input-format'

* feat/named-input-format:
  Revert "minor, translate named input formats in __trans_dtfmt() to their dfmt counterpart"
  minor, make all __trans_*() routines return the format
  minor, extradite __trans_*() operations into {date-core,time-core,dt-core}-private.h