feat: patternNot

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Description

Currently, Angular's form validation system provides Validators.pattern() to validate that a form control matches a specific regular expression pattern. However, when we need to validate that a value does NOT match a pattern, developers have to write negated regular expressions (e.g., using negative lookahead or inverse character classes).

This approach has several drawbacks:

• Writing negated regex patterns is complex and error-prone
• Negated patterns can be significantly less performant, especially for complex patterns
• The intention of the code becomes less clear and harder to maintain
• Some patterns are extremely difficult or impossible to negate correctly using regex alone

Example of current workaround:

Validators.pattern(/^(?!.*badword).+$/) // Prevents 'badword' from appearing anywhere

Proposed solution

A new validator patternNot() that validates that a form control value does NOT match the given pattern.

// Proposed API
Validators.patternNot(pattern: string | RegExp): ValidatorFn

// Usage example
formControl = new FormControl('', [
  Validators.patternNot(/badword/), // Fails if 'badword' is found
]);

Benefits:

• More intuitive API for negative pattern validation
• Better performance as it doesn't require complex negated regex
• Clearer code intention
• Easier to understand