Url helper

[risalfajar]

Describe the problem

Currently, there's no way to create a link relative to the page/layout in which it is used, all links must be absolute. This has 2 problems:

1. It's painful to write links in deeply nested page/layout, let alone if it has multiple slugs.
2. It's painful to maintain those links, since one change in the parent route can break all children links.

Describe the proposed solution

Routify resolve this nicely with Url helper.

To quote them:

$url resolves paths relative to the page/layout file in which it is used. This ensures consistent URLs that are unaffected by the current browser address (unlike normal relative URLs).
You can also call the function $url() on any page to get the current path.

We can borrow their implementation.

Alternatives considered

No response

Importance

would make my life easier

Additional Information

Related issues:
#822
#10708