lib{store,fetchers}: Pass URLs specified directly verbatim to FileTransferRequest

The URL should not be normalized before handing it off to cURL, because
builtin fetchers like fetchTarball/fetchurl are expected to work with
arbitrary URLs, that might not be RFC3986 compliant. For those cases
Nix should not normalize URLs, though validation is fine. ParseURL and
cURL are supposed to match the set of acceptable URLs, since they implement
the same RFC.

src/libutil/url.cc

@@ -434,4 +434,10 @@ bool isValidSchemeName(std::string_view s)
     return std::regex_match(s.begin(), s.end(), regex, std::regex_constants::match_default);
 }
 
+std::ostream & operator<<(std::ostream & os, const ValidURL & url)
+{
+    os << url.to_string();
+    return os;
+}
+
 } // namespace nix