Clean up, merge and update zh/zh-* translations
- mediawiki/core: Rearrange zh/zh-* fallbacks, translations, aliases in mediawiki/core
- mediawiki/extensions/Babel: Update, merge zh-tw translations back to zh-hant and recover zh-cn, zh-sg translations
- mediawiki/extensions/DPLforum: Adding zh, zh-hans, zh-hant namespace names and aliases
- mediawiki/extensions/Flow (StructuredDiscussions): Adding zh, zh-hans, zh-hant namespace names, aliases and special page names, aliases
- mediawiki/extensions/MobileFrontend: Fix incorrect special page translation in MobileFrontend
- mediawiki/extensions/Scribunto: Update zh namespace names and adding namespace aliases
- mediawiki/extensions/Widgets: Adding zh, zh-hans, zh-hant namespace names and aliases in Widgets
- operations/mediawiki-config: Clean up zh/zh-* namespace aliases