feat(expectations): add toMatchConstraint

[owenvoke]

Q	A
Bug fix?	no
New feature?	yes
Fixed tickets	#...

This allows the use of Constraint classes for more complex validation.

// From basic constraints
expect(true)->toMatchConstraint(new IsTrue());

// To more complex constraints
expect(true)->toMatchConstraint(
    $this->logicalAnd(
         $this->logicalNot(new IsFalse()),
         new IsType(IsType::TYPE_BOOL)
    )
);

// To custom constraints
expect('https://google.com')->toMatchConstraint(new IsValidUrlConstraint());

class IsValidUrlConstraint extends PHPUnit\Framework\Constraint
{
    public function toString()
    {
        return 'is a valid url';
    }

    protected function matches($other): bool
    {
        if (! is_string($other)) {
            return false;
        }

        return preg_match(
            Symfony\Component\Validator\Constraints\UrlValidator::PATTERN,
            $other
        ) > 0;
    }
}

Custom constraints should extend PHPUnit\Framework\Constraint, and provide a matches() and toString() method, and optionally override the evaluate() method.

[nunomaduro]

You can add this.

[owenvoke]

I'll add the docs for it tomorrow. 👍

pestphp/website#89