Add templates and patterns for child pages of Privacy Policy

[adamwoodnz]

The child pages of about/privacy/ were missed in the first round. They need templates and patterns in this theme to match the rest of the About sub pages.

1. https://wordpress.org/about/privacy/cookies/
2. https://wordpress.org/about/privacy/data-erasure-request/
3. https://wordpress.org/about/privacy/data-export-request/