Consolidate advanced & rich editor docs

[charrondev]

Currently we have a section called "Posting" https://docs.vanillaforums.com/help/posting/ that contains advanced editor docs.

• Update this mention https://docs.vanillaforums.com/help/posting/#advanced-editor to be about rich editor. Update screenshots in the documentation.
• Move this part of the Rich Editor documentation into /help/posting and make it generic enough to apply to both editors. Leave a note in the rich editor doc about this. https://docs.vanillaforums.com/help/addons/rich-editor/#enabling-rich-editor
• Consolidate the following documents and place them at /help/posting/advanced-editor.
  • https://docs.vanillaforums.com/help/addons/advanced-editor/
  • https://docs.vanillaforums.com/help/posting/smart-embed/
  • https://docs.vanillaforums.com/help/posting/emoji/
• Move the following document: /help/addons/rich-editor to /help/posting/rich-editor.
• Update the following document with information/screenshots involving rich editor.