Consider implement validation handler API to abstract away the FluentValidation detail

[teneko]

Currently, FluentValidation is tightly coupled to EditModelValidatorBase<TDerived>. Should we abstract it to support other validation libraries?

This would require to implement a "validation handler API".

Consequences & Ideas

• Delegate lifecycle stages and responsibilities to the validation handler:
  • Support initialization and disposal (tear-up / tear-down).
  • Resolve library-specific, possibly lifecycle-aware (e.g. disposable) validators.
  • Pull up ServiceScopeSource to the parameters transition API.
• Allow validation handlers to participate in the parameters transition API.
• Consider static vs non-static validation handlers:
  • If static, how do we manage external state resolution or storage?

Proposal

TODO