Real-time collaboration: Update "Join" action label in post list if lock expires

When RTC is enabled, let the "Join" action link in the post list turn into "Edit" after the post lock expires. Do this by rendering both "Edit" and "Join" as separate spans and toggling visibility via CSS using the `wp-collaborative-editing` class that heartbeat already manages. Do the same to aria-label with screen-reader-text spans so the accessible name stays in sync with the visible text across lock state changes.

Developed in https://github.com/WordPress/wordpress-develop/pull/11346.

Follow-up to [62074].

Props shekharnwagh.
See #64622.



git-svn-id: https://develop.svn.wordpress.org/trunk@62146 602fd350-edb4-49c9-b593-d223f7449a82