In an effort to make ThreadSettingsModal easier to work with, we're pulling general, privacy, and delete tabs out into their own separate components.
This diff does that for ThreadSettingsPrivacyTab, but in a limited way. We're basically moving over the mainContent JSX markup and prop drilling that state that's still held by ThreadSettingsModal.
Once we've extracted the JSX markup for general, privacy, and delete.. and prop drilled as necessary to keep things working as they did before: we're going to push down the state and functionality into the smaller "tab" components so things are properly encapsulated.
And once that's done, we should easily be able to turn ThreadSettingsModal into a functional component.. and refactor ThreadSettingsModal using @def-au1t's TabsContainer and TabsItem components.
Depends on D3716