URL pathname and search setter incorrectly strips trailing spaces

[Luca Casonato]

Test case:

```
const url = new URL('http://example.com/');
url.pathname = '/ ';
url.search = '? ';
url.hash = '# ';
console.log(url.href);
```

Implementations:

```
// whatwg-url@13.0.0
"http://example.com/%20?%20#%20" ✅

// Chrome 117.0.5881.0
"http://example.com/%20?%20#%20" ✅

// Firefox 114.0.2
"http://example.com/%20?%20#%20" ✅

// Safari TP 171
"http://example.com/?#%20" ❌

// Deno 1.35.0
"http://example.com/?%20#%20" ❌

// node@20.4.0
"http://example.com/%20?%20#%20" ✅
```

New tests in https://github.com/web-platform-tests/wpt/pull/40959

[Anne van Kesteren]

One somewhat tricky aspect here is that our internal URL manipulation APIs are not very aligned with the public API, which make me worry we miss certain aspects, in particular around trimming an opaque path when query and fragment become null. I will attempt some refactoring to get them closer together, starting with bug 259245. Feel free to take this however. No promises. :-)

[Radar WebKit Bug Importer]

<rdar://problem/112433299>

[Anne van Kesteren]

Pull request: https://github.com/WebKit/WebKit/pull/16020

[EWS]

Committed 266252@main (cc626f31c374): <https://commits.webkit.org/266252@main>

Reviewed commits have been landed. Closing PR #16020 and removing active labels.

[Anne van Kesteren]

*** Bug 250004 has been marked as a duplicate of this bug. ***