chore(algebra/order/group/defs): split file (#17787)
Splits:
* algebra/order/group/defs.lean
* algebra/group/with_one.lean
* algebra/order/monoid/with_zero.lean
This will get us unstuck on the mathlib4 port, moving some of the files (about algebraic morphisms and equivalences) that are currently waiting for fixes in Lean 4 off the critical path.
Co-authored-by: Scott Morrison <scott.morrison@gmail.com>
