Accept nooped plurals in wp_generate_tag_cloud() / wp_tag_cloud().

Renders topic_count_text_callback more or less obsolete. It can still be used, but passing a plural is easier.

fixes #27262. see #7989, #14424.

Built from https://develop.svn.wordpress.org/trunk@27376


git-svn-id: http://core.svn.wordpress.org/trunk@27225 1a063a9b-81f0-0310-95a4-ce76da25c4cd