Use new core URI implementation

[brendt]

See https://thephp.foundation/blog/2025/10/10/php-85-uri-extension/

[xHeaven]

Are we interested in the RFC 3986 or the WHATWG URL model? The former would be the standard, the latter would be the browser-like parsing.

[brendt]

Definitely browser-like

[boydbloemsma]

Can I pick this up?

[brendt]

Yes :)

[boydbloemsma]

While working on this issue I hit something that I'd like to settle before updating tests, WHATWG never produces an empty path.
Any URL with authority gets / as its path, so:

Uri::from('https://example.com?foo=bar')->toString();
// before: 'https://example.com?foo=bar'
// after: 'https://example.com/?foo=bar'

Uri::from('https://example.com')->path;
// before: null
// after: '/'

So we basically have two options:

1. Accept WHATWG behavior since it's what browsers do, and create a small breaking change.
2. Map / back to null preserving current output.

My preference is option 1.

[brendt]

Definitely 1, I'd even say the current behaviour is a bug :D