Improve inline documentation for `Walker_Nav_Menu`, `Walker_Nav_Menu_Edit`, `Walker_Nav_Menu_Checklist`.

Includes previously undocumented parameters.

See #23406.

Built from https://develop.svn.wordpress.org/trunk@25643


git-svn-id: http://core.svn.wordpress.org/trunk@25560 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Improve inline documentation for the `Walker` class.

Includes previously undocumented parameters.

See #23406.

Built from https://develop.svn.wordpress.org/trunk@25644


git-svn-id: http://core.svn.wordpress.org/trunk@25561 1a063a9b-81f0-0310-95a4-ce76da25c4cd