General: Rename the `$new_whitelist_options` global variable.

This change renames `$new_whitelist_options` to `$new_allowed_options`. This makes the variable’s purpose more clear, and promotes using more inclusive language.

For backwards compatibility, the new variable is passed by reference to the old one.

Follow up to [48121].

Props ayeshrajans, desrosj, jorbin, SergeyBiryukov.
See #50413.
Fixes #50434.
Built from https://develop.svn.wordpress.org/trunk@48477


git-svn-id: https://core.svn.wordpress.org/trunk@48246 1a063a9b-81f0-0310-95a4-ce76da25c4cd