Reconciling Data.Nat.Divisibility.Core._∣_ and Algebra.Definitions.RawMagma._∣_

[jamesmckinna]

See the discussion on issue #1919.

Two Three parts to this:

• low-hanging fruit: added pattern synonym and consequences/uses of it to Data.Nat.*
• higher-hanging fruit: reconcile the two definitions of _∣_ for the Data.Nat.Base.*-rawMagma instance
• knock-on changes for Data.Integer.Divisibility.* and Data.Rational.* only if the preceding step succeeds

Proposal: merge the low-hanging fruit one now, and keep this branch, and the above checkboxes, open for a subsequent independent PR. In the meantime, a chance to think about the pro/contra proposals regarding how to reconcile the various definitions...

[JacquesCarette]

The code up to this point of completion makes sense to me and seems to be a clear improvement.

[jamesmckinna]

Label status:ready as a placeholder for 'enough commits from my side' ;-)

[JacquesCarette]

Continues to be nice.