[11.x] Conditional Validation for Fluent Email Rules

[SanderMuller]

Add Conditional Validation for Fluent Email Rules

This PR enhances the Email validation rule in Laravel by introducing conditional validation capabilities. It allows developers to dynamically enable or disable specific email validation rules, making the validation logic more flexible and adaptable to specific use cases.

Key Features:

• Unset Default Rules: Developers can now unset default Email::default() rules, such as disabling MX record validation for certain routes. This is particularly useful for cases like Single Sign-On (SSO) emails without inboxes.
• Dynamic Rule Application: Rules can now be conditionally applied using closures, enabling context-specific validation logic, such as skipping DNS checks for whitelisted email domains.

Key Changes:

• Updated the Email class to accept bool|Closure conditions for rules like rfcCompliant, validateMxRecord, preventSpoofing, and withNativeValidation.
• Modified the buildValidationRules method to evaluate conditions dynamically based on the provided attribute and value.
• Added extensive tests in ValidationEmailRuleTest to ensure the new functionality works as intended for various scenarios.

Benefits:

• Increased Flexibility: Developers can customize email validation rules based on the context, such as bypassing specific checks for certain email patterns or routes.
• Enhanced Use Case Support: Scenarios like SSO emails or whitelisting specific domains are now easier to handle.
• Backward Compatibility: Existing behavior remains unchanged unless conditional logic is explicitly applied.

This update aligns with Laravel's focus on making validation rules expressive and adaptable while maintaining backward compatibility.

[shaedrich]

Furthermore, it would be interesting, yet not easily implemented with the current implementation, if the method didn't only return whether to apply a specific rule but also if the more general rule should be applied with a flag (in this case strict). Implementing this by making the first param of the setter function bool|\Closure(): bool as well, would be one option, only passing in bool|Closure(): RfcComplianceEnum|null $condition another.

Our hypothetical RfcComplianceEnum would look something like this:

enum RfcComplianceEnum
{
    case Loose; // or Basic
    case Strict;
}