Introduce a sitemeta filter for populate_network

[jeremyfelt]

populate_network() can be used by a plugin to help create new networks in a multisite environment if wp-admin/includes/schema.php is loaded in as needed. As it stands now, much of the information added to the database by populate_network() is hard coded and cannot be modified as networks are created through other sources.

The attached patch adds a filter on the $sitemeta array to allow a plugin to modify network defaults before they are added to the DB. Some cleanup is also done on the formatting of the original array.

[nacin]

Looks good. wp_parse_args() is however not needed. And again the @var statements are not really our style. :-)

[jeremyfelt]

25020.2.diff​ takes out wp_parse_args() and the type hinting

Replying to nacin:

And again the @var statements are not really our style. :-)

Yet... :)

[nacin]

In 25414:

Add populate_network_meta filter to populate_network().

props jeremyfelt.
fixes #25020.