Add fallback for Config\Cookie

[paulbalandan]

Description
Fixes #4619

Checklist:

• Securely signed commits

[sfadschm]

Dumb question which might be related:
If someone sees this in Config\App :

CodeIgniter4/app/Config/App.php

Line 245 in aff1f3a

* @deprecated use Config\Cookie::$prefix property instead.

and decides to use Config\Cookie instead as suggested then goes on and deletes the property from App\Config, he will get an error from HTTP\Response:

CodeIgniter4/system/HTTP/Response.php

Lines 161 to 164 in aff1f3a

	$this->cookiePrefix = $config->cookiePrefix;
	$this->cookieDomain = $config->cookieDomain;
	$this->cookiePath = $config->cookiePath;
	$this->cookieSecure = $config->cookieSecure;

Should these assignements not try to read the (deprecated) property from Config\App and if it is not there, get it from Config\Cookie? Like done here:

CodeIgniter4/system/Security/Security.php

Line 140 in aff1f3a

$cookiePrefix = $cookie->prefix ?? $config->cookiePrefix;

[paulbalandan]

IMO, it is not the framework's problem. Those properties are only deprecated, so technically they are still supported until the next major. If anyone deletes them intentionally then they are inflicting upon themselves their own breaking changes. The cost of providing workarounds for possible removal of deprecated members in userland then removing those workarounds in next major version is not worth the benefit.

[paulbalandan]

Those assignments in Response are practically useless as those aren't used anymore. Those are there for the sake of BC preservation for users still using them.

[sfadschm]

Alright, I guess I misunderstood the principle of deprecations. However, still feels weird that this seems to be handled differently across the framework.