[php-src] Issue #8489: Add additional methods for reflections that have attributes

Issue: https://github.com/php/php-src/issues/8489 Author: ollieread ### Description All currently attributable reflections have a single method relating to attributes. ``` getAttributes(?string $name = null, int $flags = 0): array ``` Additional methods for dealing with attributes would be a nice improvement and would simplify common approaches. I'm proposing the following methods. ## getAttribute Get a single instance of ReflectionAttribute, following the same rules as getAttributes, minus the fact that $name is required. ``` getAttribute(string $name, int $flags = 0): ?ReflectionAttribute ``` If more than one attribute matches, an exception should be thrown. ## hasAttribute Functionally identical to getAttribute, except it will return true if one or more matches are found, otherwise it returns false. ``` hasAttribute(string $name, int $flags = 0): bool ``` ## getNumberOfAttributes Again, follows the same rules as getAttributes, but will return the number found. This particular method is based on the [ReflectionFunctionAbstract::getNumberOfParameters method](https://www.php.net/manual/en/reflectionfunctionabstract.getnumberofparameters.php). ``` getNumberOfAttributes(?string $name = null, int $flags = 0): int ```