Inline documentation improvements for `Walker_Category` and `Walker_CategoryDropdown`.

Also covers previously undocumented parameters.

See #23406, #19249.


git-svn-id: https://develop.svn.wordpress.org/trunk@25641 602fd350-edb4-49c9-b593-d223f7449a82
Inline documentation for `Walker_Category_Checklist`.

See #23406.


git-svn-id: https://develop.svn.wordpress.org/trunk@25642 602fd350-edb4-49c9-b593-d223f7449a82