Mark the <rb> element with partial_implementation for Chrome and Safari (#6613)
Mark the <rb> element with partial_implementation for Chrome and Safari (#6613)

This change marks the <rb> element with partial_implementation for
Safari and Chrome and all Blink/Chrome-based browsers. It also adds a
note explaining what’s partially implemented and what’s not.

Fixes https://github.com/mdn/browser-compat-data/issues/6475

Co-authored-by: Joe Medley <e5f32d9ca37888f2e401c8370536acae62d3b209@google.com>
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data