Url::make_relative unconditionally strips trailing `/`

• Note that this crate implements the URL Standard not RFC 1738 or RFC 3986

join and make_relative are presented as inverse functions. However, make_relative strips the trailing / when asked to make a directory relative to some base. For example: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=5da4403820faf5f73ad79ac9c2e4ef1c

This is rather unexpected since join makes a point to remind the user how significant trailing / are since they indicate the url refers to a directory. Essentially, you cannot:

let base = Url::parse("file:///base/")?;
let url = base.join("directory/")?;
let directory = base.make_relative(&url)?; // yields "directory" sans `/`

I ran into because I'm actually trying to construct a relative directory url given an absolute file url and cannot seem to figure out a way to do so without manually checking for a trailing / and adding it back.

The affected entry point is Url::make_relative; compare its result with Url::join using the file:///base/ and directory/ example. Trace how trailing slashes are handled, then verify that making the joined directory URL relative preserves the slash and keeps the two operations consistent.