[RFC] Standard size of reference widgets

Reference: https://github.com/nextcloud/spreed/issues/14506

Issue

We don't know the size of reference widget to be rendered beforehand, so it causes jumping:

• NcRichText parses the text, and detects a link -> loading starts (~30px for a spinner)
• Server can return null if widgets are disabled, or service is inaccessible -> render nothing (shrink to 0px)
• OR it renders a simple link (~70px)
• OR it renders a link with image preview (~120px)
• OR it renders a conversation link (~220px)
• OR it renders a custom widget (any size possible)

Ideas

• Use standard size for all widgets
  • Interactive wigets size should be unaffected, but non-interactive appearance should comply with the size set
• Preload information with the context (e.g Talk message object) (on app side)
  • caching issues, valiation issues, request size, relying on server accessibility
• Pass height prop to registerWidget if custom (on app side)
  • always in the browser
  • component doesn't know from a link, which widget would be rendered, and which size taken
  • provide information (reference widget key) or parsing method to try derive richObjecType on client before actually reaching the server
• Add option to disable widgets at all (on app side)
  • Not a real solution, but alternative

Start by reading the linked spreed issue and this RFC, then inspect the NcRichText flow and the registerWidget API mentioned here. Compare the listed widget outcomes and decide on a concrete, agreed approach for preventing layout jumps. Done means a settled specification for standard sizing or another selected solution, including how custom and disabled widgets behave.