Add support for per-directory `+hooks.server.js` route files

Describe the problem

The current hooks functionality is really useful, particularly when used with sequence() to create an event pipeline. However, I'm increasingly finding that I want to specialise hooks for a given request paths, which requires pathname checking. Whilst this works, it is brittle - changing the route folder requires changing the pathname check. It would be preferable to colocate specialised hooks with the routes they pertain to.

Describe the proposed solution

I would like to be able to add a +hooks.server.js (or .ts) route file to a route folder that would export server hooks specifically for that route and its children. The request event handler would call the exported handle function after the current hooks.server handle function had been called, effectively appending it to the global hook sequence.

Where a child route folder has parent route folders with hooks, these would be appended prior to any hooks specific to the child.

Alternatives considered

Prior to the introduction of generated types I had used an interceptor pattern to wrap Handle and / or RequestHandler, but this has become too unwieldy to type correctly, and has resulted in unnecessary boilerplate-like code.

Importance

would make my life easier

Additional Information

No response

Start by reading the current hooks.server handling and the request event handler. Trace how route folders and parent-child relationships are resolved; done means per-directory +hooks.server.js or .ts files apply to their route and children, with parent hooks appended before child hooks and after the global hook.