Migrate SKIPIF -> EXTENSIONS (#7138)

This is an automated migration of most SKIPIF extension_loaded checks.

Update ext/sockets parameter names

Also change $max_length to $length in a number of filesystem APIs,
where our usage was inconsistent.

Closes GH-6276.

Convert resources to objects in ext/sockets

Closes GH-5900.

Properly handle non resources passed to socket_select()

As of PHP 8.0.0, failing `zend_fetch_resource_ex()` throws a TypeError,
so we cannot simply skip non resources in the `$read`, `$w

Properly handle non resources passed to socket_select()

As of PHP 8.0.0, failing `zend_fetch_resource_ex()` throws a TypeError,
so we cannot simply skip non resources in the `$read`, `$write` and
`$except` arrays. Instead we bail out. Since these arrays are already
checked in `php_sock_array_to_fd_set()`, we remove the additional check
in `php_sock_array_from_fd_set()`.

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