Allow using the `$network_id` parameter of `get_blog_count()` again

[flixos90]

The $network_id parameter of get_blog_count() has not been used since 3.1, and was officially deprecated in 25113. When looking at the history, it appears that this was done to be able to fully rely on get_site_option() which does not support passing a network ID.

However, now we have get_network_option() which _does_ support a network ID, so I think we should un-deprecate this parameter and make use of it again (is that possible?).

[flixos90]

37865.diff​ makes use of the parameter again, by leveraging the power of get_network_option(). In the DocBlock, I also added notices for both the 3.7 change (previously missing) and the new change.

[flixos90]

An alternative approach could be:

• introduce get_network_site_count( $network = null ) (returns the value of the network option blog_count)
• introduce get_global_site_count() (returns the sum of get_network_site_count() for all networks)
• deprecate get_blog_count() and recommend get_network_site_count() as replacement
• replace Core usages of get_blog_count() with either get_network_site_count() or get_global_site_count() (depending on context)

Related to this ticket: #37866

[jeremyfelt]

Nice one. It's fun to see the history on the deprecation.

I think the approach in 37865.diff​ makes sense for the time being. Since we aren't actually adding any new functionality, we should stick with the same name (get_blog_count()). In the future, if we think of something super interesting to do with a new version of the function, we may want to explore a get_site_count().

get_global_site_count() could be interesting once we have a better idea of what global options look like.

[flixos90]

37865.2.diff​ adjusts the version number and the docblock to be more precise (see https://core.trac.wordpress.org/ticket/37866#comment:5 for a related comment).

[flixos90]

37865.3.diff​ adds a unit test for the new parameter. Another (rather unstable) unit test was adjusted in order to work with an additional network being registered in wpSetUpBeforeClass().

[flixos90]

In 40370:

Multisite: Support the $network_id parameter of get_blog_count().

The get_blog_count() function used to support an $id parameter for the network ID prior to WordPress 3.1. This parameter has not been used since the introduction of get_site_option() and was later deprecated in [25113]. With get_network_option() however it is possible to support the parameter again, now properly renamed as $network_id.

A unit test has for the parameter has been added as well. Another unit test in the same class was adjusted to work properly with multiple networks existing.

Fixes #37865.