Fix and enhance comment editor monospace toggle

[silverwind]

Fixes: #36175

1. Correctly apply setting on textareas spawned by comment edit
2. When changing the setting, apply it to all textareas on the current page and in all other open tabs

[silverwind]

I think this could be expanded to also apply the setting in other open tabs by leveraging the storage event:

https://developer.mozilla.org/en-US/docs/Web/API/Window/storage_event

I guess a small storage helper module is needed to abstract this out of the file and be useful for all localStorage-backed variables.

[silverwind]

I've added the bare minimum to get the setting working across tabs too. There's probably an opportunity to abstract into some localStorage module suitable for more similar localStorage-backed settings, but I'm not totally certain how to design it.

[silverwind]

web_src/js/modules/storage.ts is now contains minimal localStorage wrapper functions and I've used them everywhere where we previously used localStorage directly (except inline scripts, but that's another topic to be solved via web components). This is in preparation so that these settings can be synced to the server in the future.