Discuss V7 deprecations

[DannyvdSluijs]

This discussion is to keep track of possible deprecations for V7. Feel free to contribute with feedback, suggestions for new deprecations and anything related to deprecations in V7.
Once a deprecation is decided final it should be marked as such in V6 before we can remove in V7.

Drop support for associative arrays

Status: undecided
Description: Associative arrays have been troublesome for some time. We aren't explicit in what we do or do not support. Resulting in discussions as we can see in #767, #780, #784, #786

Drop nullable support for $schema in Validator::Validate

Status: undecided
Description: As it seems a schema should always be required, also see #541

Drop Validator::coerce

Status: undecided
Description: As mentioned in code this method is there for backwards-compatibility with the previous api which means we could drop it in the next mayor version. This method is also explained in the README.md which then should also be removed.

Drop support for inline schemas

Status: undecided
Description: As mentioned by @shmax in #541 (comment) we are currently supporting inline array of objects for the $schema property which isn't allowed accordingly to the specs. These inline schemas seems to be supported since one of the earliest versions of 17 years ago which even pre-dates the official JSON schema specifications (Draft 0 is dated 2009-12-05)

Drop support for date time offsets without a colon

Status: undecided
Description: As mentioned by @matason in #838 (comment) an offset without a colon in date time is not part of the offical RFC.

Drop SchemaStorage::getUriRetriever and SchemaStorage::getUriResolver

Status: undecided
Description: Both methods are unused (with the exception of tests) and exposes the internal working of the schema storage allowing for mutability error types