[Sync EN] uri: Add description to all Exceptions

PR: `https://github.com/php/doc-en/pull/5466` (2026-04-06)

**Nouveaux fichiers EN (pas encore traduits)**
- `reference/uri/book.xml`
- `reference/uri/uri.invaliduriexception.xml`
- `reference/uri/uri.urierror.xml`
- `reference/uri/uri.uriexception.xml`
- `reference/uri/uri.whatwg.invalidurlexception.xml`

