[Admin] Remove validation related methods

[tambait]

Subject

Closes #6233

Changelog

### Changed
- Changed `AbstractAdmin::buildForm()` removed line with call to `addEventListener()` which used `preValidate()`

### Removed
- Removed `AdminInterface::validate` method specification
- Removed `AbstractAdmin:validate` method implementation
- Removed `AbstractAdmin::attachInlineValidator()` method
- Removed `AbstractAdmin::preValidate()` method
- Removed `AdminExtensionInterface::validate()` method specification
- Removed `AbstractAdminExtension::validate()` method implementation

[VincentLanglet]

@tambait In order to reduce conflict, you should always wait for the merge in 3.x, then for the 3.x merge into master before doing the PR in master

[SonataCI]

Could you please rebase your PR and fix merge conflicts?

[SonataCI]

Could you please rebase your PR and fix merge conflicts?

[VincentLanglet]

I would say you can also remove

• The property protected $validator; of the AbstractAdmin
• The set/getValidator method of the AbstractAdmin and the interface
• All the 4 class_exists(\Sonata\Form\Validator\ErrorElement::class); occurences
• ->scalarNode('validator')->defaultNull()->end() in DependencyInjection/Configuration
• All the validator occurence in the doc
• All the 'validator' occurence in AddDependencyCallsCompilerPass

[tambait]

* All the 4 class_exists(\Sonata\Form\Validator\ErrorElement::class); occurences

I don't see these appearing in the master branch only in 3.x, so should I just add notice in 3.x for this to be removed in next major?

Also, should Command\Validators be removed or modified in any way?

[VincentLanglet]

I don't see these appearing in the master branch only in 3.x, so should I just add notice in 3.x for this to be removed in next major?

If it's already removed, nothing to do ;)

Also, should Command\Validators be removed or modified in any way?

I don't think so. These validators are used for the commands, not the admin.

[SonataCI]

Could you please rebase your PR and fix merge conflicts?

[franmomu]

Sorry @tambait 🙏 I didn't see this PR before creating #6644, I just wanted to remove a comment that should be there and I ended up removing other NEXT_MAJOR comments because there were fails with phpstan.

[VincentLanglet]

Sorry @tambait 🙏 I didn't see this PR before creating #6644, I just wanted to remove a comment that should be there and I ended up removing other NEXT_MAJOR comments because there were fails with phpstan.

Is there still something to keep in this PR ?

[tambait]

Sorry @tambait pray I didn't see this PR before creating #6644, I just wanted to remove a comment that should be there and I ended up removing other NEXT_MAJOR comments because there were fails with phpstan.

Is there still something to keep in this PR ?

@VincentLanglet
I switched from working on this PR because there were things to be done on related PR #6633 on 3.x branch

[VincentLanglet]

Oh yes indeed, let's ask @franmomu A review for your PR introducing deprecations :p