Closes https://github.com/curl/curl/pull/6920

When the host name in a URL is given as an IPv4 numerical address, the
address can be specified with dotted numericals in four different ways:
a32, a.b24, a.b.c16 or a.b.c.d and each part can be specified in
decimal, octal (0-prefixed) or hexadecimal (0x-prefixed).

Instead of passing on the name as-is and leaving the handling to the
underlying name functions, which made them not work with c-ares but work
with getaddrinfo, this change now makes the curl URL API itself detect
and "normalize" host names specified as IPv4 numericals.

The WHATWG URL Spec says this is an okay way to specify a host name in a
URL. RFC 3896 does not allow them, but curl didn't prevent them before
and it seems other RFC 3896-using tools have not either. Host names used
like this are widely supported by other tools as well due to the
handling being done by getaddrinfo and friends.

I decided to add the functionality into the URL API itself so that all
users of these functions get the benefits, when for example wanting to
compare two URLs. Also, it makes curl built to use c-ares now support
them as well and make curl builds more consistent.

The normalization makes HTTPS and virtual hosted HTTP work fine even
when curl gets the address specified using one of the "obscure" formats.

Test 1560 is extended to verify.

Fixes #6863
Closes #6871

... by fixing macros to do-while constructs and moving out the calls to
"break" outside of the actual macro. It also fixes the problem where the
macro was used witin a loop and the break didn't do right.

Reported-by: Emil Engler
Fixes #6847
Closes #6909

No longer considered experimental.

Closes #6700

... previously they were supported if a TLS library would (unexpectedly)
still support them, but from this change they will be refused already in
curl_easy_setopt(). SSLv2 and SSLv3 have been known to be insecure for
many years now.

Closes #6773

Closes #6901

Pointed out by scan-build

Closes #6900

The code in cr_recv was returning prematurely as soon as the socket
reported no more data to read. However, this could be leaving some
unread plaintext data in the rustls session from a previous call,
causing causing the transfer to hang if the socket never receives
further data.

We need to ensure that the session is fully drained of plaintext data
before returning CURLE_AGAIN to the caller.

Reviewed-by: Jacob Hoffman-Andrews
Closes #6894

Add test 676 to verify that setting CURLOPT_COOKIEFILE to NULL again clears
the cookiejar from memory.

Reported-by: Stefan Karpinski
Fixes #6889
Closes #6891

Fixes #6864
Cloes #6886