Add new internal `curl_url_same_origin()` to check if a href has the
same origin as a base URL. Add test cases in test1675 and use this in
http2 push handling.
Closes#21328
There is no reason we should treat this part different on Windows. Noe
anything except blank, localhost or 127.0.0.1 cause error there as well.
Also: fix query handling in urlencode_str
Closes#21296