Correctly remember last url when multiple blocks are on the same page

[psrpinto]

When multiple blocks are on the same page, in different screens (e.g. different rooms), refreshing the page would not correctly bring each block to the screen where they were previously on.

This PR fixes that by introducing an instanceId attribute which is unique for each block on a page. We then use that instanceId to namespace the chatrix_last_url_hash property in local storage, so that it becomes chatrix_abc123_last_url_hash (where abc123 is the instanceId).

Note: For blocks created before this PR, the pages will need to be re-saved for the block(s) to get an instanceId.

Screen recording

Screen.Recording.2023-04-17.at.16.34.20.mov

[ashfame]

🚀

[akirk]

@psrpinto researched using Gutenberg's own client ID (UUID for blocks) but the problem with that is that it changes between saves, the instanceID will remain the same throughout the block's life.