Update symfony/validator requirement from ^3.0 to ^4.3

[dependabot-preview]

Updates the requirements on symfony/validator to permit the latest version.

Changelog

Sourced from symfony/validator's changelog.

4.3.0

• added Timezone constraint
• added NotCompromisedPassword constraint
• added options iban and ibanPropertyPath to Bic constraint
• added UATP cards support to CardSchemeValidator
• added option allowNull to NotBlank constraint
• added Json constraint
• added Unique constraint
• added a new normalizer option to the string constraints and to the NotBlank constraint
• added Positive constraint
• added PositiveOrZero constraint
• added Negative constraint
• added NegativeOrZero constraint

4.2.0

• added a new UnexpectedValueException that can be thrown by constraint validators, these exceptions are caught by
  the validator and are converted into constraint violations
• added DivisibleBy constraint
• decoupled from symfony/translation by using Symfony\Contracts\Translation\TranslatorInterface
• deprecated ValidatorBuilderInterface
• made ValidatorBuilder final
• marked format the default option in DateTime constraint
• deprecated validating instances of \DateTimeInterface in DateTimeValidator, DateValidator and TimeValidator.
• deprecated using the Bic, Country, Currency, Language and Locale constraints without symfony/intl
• deprecated using the Email constraint without egulias/email-validator
• deprecated using the Expression constraint without symfony/expression-language

4.1.0

• Deprecated the checkDNS and dnsMessage options of the Url constraint.
• added a values option to the Expression constraint
• Deprecated use of Locale constraint without setting true at "canonicalize" option, which will be the default value in 5.0

4.0.0

• Setting the strict option of the Choice constraint to anything but true
  is not supported anymore.
• removed the DateTimeValidator::PATTERN constant
• removed the AbstractConstraintValidatorTest class
• removed support for setting the checkDNS option of the Url constraint to true

3.4.0

... (truncated)

Commits

• 6ad0600 Fix tests
• 81da1cf Reference individual contracts packages
• 1511d0f Merge branch '4.2' into 4.3
• 01966bc bug #31481 [Validator] Autovalidation: skip readonly props (dunglas)
• 90f8636 Drop useless executable bit
• 7ebf976 [Validator] Autovalidation: skip readonly props
• 32cc317 Fix finding parent definition
• a8e33e3 Merge branch '4.2'
• 322339a feature #31060 [Validator] Make API endpoint for NotCompromisedPasswordValida...
• e47f7d9 [Validator] Make API endpoint for NotCompromisedPasswordValidator configurable
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #56.