Set $current_user global in wp_signon() after successful authentication

[fjarrett]

The $current_user global should be set after successful authentication inside wp_signon() instead of waiting for the next load of WordPress.

Although the $user_login string and $user object are passed through the wp_login hook, there are some functions that don't allow user parameters and rely solely on get_current_user_id(), such as wp_destroy_other_sessions().

This is easy enough to work around, but it seems reasonable to expect that user-related function calls should "just work" at any point after authentication.

<?php

add_action( 'wp_login', function ( $user_login, $user ) {

        var_dump( get_current_user_id() ); // int(0)

        $GLOBALS['current_user'] = $user;

        var_dump( get_current_user_id() ); // int(1)

        exit;

}, 10, 2 );

[ocean90]

See #28116 and #35488 for why this is more of a documentation issue than an actual bug.