Fixes for hooks documentation on xmlrpc.php.

Adds spacing, changes an `@see` to `@link`, adds a docs-specific variable for a parameter.

See #26869, #25229 and [25281].


git-svn-id: https://develop.svn.wordpress.org/trunk@27146 602fd350-edb4-49c9-b593-d223f7449a82