Allow SchemaCompositions to be added as property

[captnCC]

Hi,
SchemaCompositions can be used on objects that have a schema property, but it is not possible to use them as a property in another Schema. The OpenApi Spec itself supports this usage.

[randelsr-vault]

This. We should be able to use AllOf to help compose schemas.

I hacked into this with a fork. Wasn't sure if this is entirely correct otherwise it would be a PR:

goldspecdigital\oooas\src\Objects\Schemas.php

    /**
     * @param Schema|SchemaComposition ...$properties
     * @return static
     */
    public function properties(Schema|SchemaComposition ...$properties): self
    {
        $instance = clone $this;

        $instance->properties = $properties ?: null;

        return $instance;
    }

Seems the correct implementation would be to leverage \GoldSpecDigital\ObjectOrientedOAS\Contracts\SchemaContract but while that works, it doesn't seem to be fully implemented yet?

[matthew-inamdar]

I'll look at implementing this in the next major release where we can leverage union types.

Edit: As we'll be dropping 7.x support.