Provide base "Simplified" and "Traditional" Chinese locales

Summary:
Fixes T11249. From what I can tell, the locale tree for Chinese looks like this in modern usage (maybe?):

• zh_Hans Chinese (Simplified)
  • zh_ZH Chinese (Simplified, China)
  • zh_SG Chinese (Simplified, Singapore)
• zh_Hant Chinese (Traditional)
  • zh_TW Chinese (Traditional, Taiwan)
  • zh_HK Chinese (Traditional, Hong Kong)

Except that everyone disagrees and does different things and various standards define esoteric things like "zh-Hans-SG".

But I think inheriting them like this mostly makes sense, probably.

This just adds the base locales; we can add the child locales later to distinguish regional variance like "color" vs "colour".

Test Plan: Saw both options in the translation menu.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11249

Differential Revision: https://secure.phabricator.com/D16212