[Core] "Node Factory" system

[kbond]

This package provides 3 node types out of the box: Directory, File and Image. It's possible that users may want other node types in the future, each with their own set of metadata/functionality. Some possible examples: Pdf, Video, Audio.

While if enough users request a specific type, we would add to core, but some kind of extension system could be developed via a NodeFactory concept to allow 3rd party nodes.

Some ideas:

/**
 * @template T of Node
 */
interface NodeFactory
{
    /**
     * @return T
     */
    public function createFrom(Node $node): Node;
}

Change Filesystem::node() method:

interface Filesystem
{
    /**
     * @template T of Node
     *
     * @param class-string<T> $type
     *
     * @return T
     */
    public function node(string $path, string $type = Node::class): Node;
}

Add Node::ensure() method:

interface Node
{
    /**
     * @template T of Node
     *
     * @param class-string<T> $type
     *
     * @return T
     */
    public function ensure(string $type): Node;
}

Once such functionality exists, the existing 1st party image support could be extracted into a dedicated zenstruck/filesystem-image package. This would leave File and Directory as the only node-types provided by the core library.