Namely:

• Make AbstractFieldValidatorFactory accept interface FieldValidatorDefinition param type
• Remove usages of concrete ConfiguredFieldDefinition in complex-fields, use interface FieldDefinition instead
  • set readOnly-ness on local fields directly (vs. on sub-field definition)
  • acknowledging minor API incompatibility in MultiValueFieldDefinition#getField()'s return type (similar for composite)

I crafted these couple commits some time ago, they were considered to go with MGNLUI-3758, but I decided to kick them out to keep things simple (and safer on 5.4).

Commits can be seen on my branch (by the time I emit the PR)
https://git.magnolia-cms.com/users/mgeljic/repos/ui/compare/commits?sourceBranch=refs%2Fheads%2FMGNLUI-3758-remove-usages-of-abstractfieldfactory-s