add_rewrite_tag() should take same params as WP_Rewrite::add_rewrite_tag()

[duck_]

The function and instance method have different signatures:

add_rewrite_tag( $tagname, $regex )

vs.

WP_Rewrite::add_rewrite_tag( $tag, $pattern, $query )

add_rewrite_tag() should have a third parameter too.

See: #2433 and [3638]

[duck_]

Might want to consider making the parameter names the same as well for extra consistency.

Also related #14546.

[scribu]

Here's my pet ticket related to improving the rewrite API: #16840

[duck_]

With matching parameter names

[duck_]

In [19756]:

Add the $query parameter to add_rewrite_tag() so that it matches WP_Rewrite::add_rewrite_tag(). Fixes #19871.

Also rename some other parameters so that they all match.