Unify headers already sent/session already started error handler (#16451)

* Unify headers already sent errors

Now whenever we need to check where headers were already sent in
ex

Unify headers already sent/session already started error handler (#16451)

* Unify headers already sent errors

Now whenever we need to check where headers were already sent in
ext/session, we call a single location that prints where, keeping it
consistent output wise.

* Unify session aready started errors

Similar to the one for headers.

* Also change session active checks too

This usually go hand in hand with the headers already sent checks, but
is in a separate commit because of the amount of tests it changes.

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Use php_error_docref() instead of zend_error() in session.c (GH-15505)

Using `php_error_docref()` is preferable since it outputs additional
details (which function has been called and wh

Use php_error_docref() instead of zend_error() in session.c (GH-15505)

Using `php_error_docref()` is preferable since it outputs additional
details (which function has been called and whether it is a startup or
shutdown error), uses HTML markup, and also provides a link to the
documentation, if configured.

Since these deprecation warnings have been introduced recently[1][2],
i.e. for PHP 8.4, there are no BC concerns.

[1] <https://github.com/php/php-src/commit/e8ff7c70f9669f1a54c47c018ccc0f80bc0c929b>
[2] <https://github.com/php/php-src/commit/b36eac94d26bdced150d9d2178f6209893d9961f>

Co-authored-by: Máté Kocsis <kocsismate90@gmail.com>

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Deprecate calling session_set_save_handler() with more than 2 arguments

Restructure ext-session tests

And small improvements to some