[ refactor ] fixes #2568; proves full symmetry for Bijection

[jamesmckinna]

A comprehensive overhaul building on the proposed refactoring in #2568 . Finally finished, I think!

UPDATED: now all 'done', and a lot tighter/smoother/cleaner

• refactor Function.Consequences? (check implicit/explicit bindings of lemmas there, esp. in their use later)
• BUT: full symmetry for Bijection now proved, old weaker form sym-≡ etc. now deprecated (this was a bug!)
• AND can prove Congruent ≈₂ ≈₁ section outright under similar equational assumptions!
• HENCE: in Function.Construct.Symmetry
  • indeed, can remove hypothesis of Congruent ≈₁ ≈₂ f from {injective|bijective}
  • hence, symmetry of IsBijective, and of Bijection, without detour via Inverse

TODO:

• CHANGELOG
• refactor Function.Construct.Symmetry Function.Properties.Bijection to prove full symmetry of IsBijective etc.

NB.

• the deprecations considered in [ DRY ] Refactor Function.* to rationalise the existence of a section to a given Surjective f #2568 are optional, it's more a case of agreeing the 'right' names; existing commits make the change so as to highlight where the work has happened
• the other changes above do necessitate deprecations, of the former, weaker (!), proofs
• these are badged as v2.3 deprecations in favour of *WithoutCongruence constructions, but a v3.0 cleanup PR would remove the old proofs entirely and rename to remove that suffix
• not entirely sure I've quite got the deprecation messages correct, given how gnarly the refactoring has been.... it's typically not a straightforward like-for-like deprecation, because the types have changed
• likewise, there may still be one or two outstanding DRY opportunities for further refactoring, but downstream!

[jamesmckinna]

Ooops! Need to fix the version number in deprecation warnings. Will fix tomorrow.

[jamesmckinna]

So I now think that the only conceivable change I might make would be to call this from rather than section:

• pro from : consistency with usage elsewhere as the counterpart to to
• con from : possible clash of names if scopes are opened carelessly?
• pro section: name standardised apart from others; standard (category-theoretic) nomenclature
• con section: too occult a name wrt the rest of the library?

[jamesmckinna]

Should this module be lifted out from Consequences to the top-level of Function.*? Or somewhere else?