Add access modifiers to methods/members in `Walker_Category` and `Walker_CategoryDropdown`.

See #27881, #22234.


git-svn-id: https://develop.svn.wordpress.org/trunk@28504 602fd350-edb4-49c9-b593-d223f7449a82
Add access modifiers to methods/members in `WP_Feed_Cache`, `WP_SimplePie_File`, and `WP_Feed_Cache_Transient`.

See #27881, #22234.


git-svn-id: https://develop.svn.wordpress.org/trunk@28505 602fd350-edb4-49c9-b593-d223f7449a82