username/password are not inherited from base URL

[Sebmaster]

The test cases and the spec have different behaviour here, I think...

new URL("/some/path", "http://user@example.org/smth").href === "http://user@example.org/some/path" according to tests, but an implementation according to spec leads to "http://example.org/some/path".

Fixes are needed (at least) in the RELATIVE state and the RELATIVE_SLASH state. Looks like this in code. Example failures from the tests here.