Add unfinished-comments feature

[cheap-glitch]

Thanks for contributing! 🍄

1. LINKED ISSUES: Closes Notify the user of unfinished comments in a tab #3680

2. TEST URLS:

• Notify the user of unfinished comments in a tab #3680
• Add git-checkout-pr feature #3596 (hidden textareas)

3. SCREENSHOT:
   

Notes:

• I used the visibilitychange event instead of pageshow/pagehide as the latter weren't working for me in Firefox. As an added bonus, it also works when hiding/minifying the whole browser window.
• I followed the suggestion of the issue for the notification text, but imho something shorter would be better, e.g. (+) or [*] (akin to what editors show when a file has been modified but not saved).

[fregante]

Thank you!

[cheap-glitch]

What do you think about using a shorter text for the indicator (e.g. [+])? It hides less of the original tab title — but on the other hand it's also less noticeable.

[fregante]

I suggested the extended text because anything else doesn’t give enough information about what’s going on, especially since this isn’t a GitHub feature. Ideally you want to go back to the tab as soon as possible and finish the comment anyway.

[fregante]

Gifs/screenshots are more helpful when they include some context. You can use this:

[fregante]

This unfortunately also catches comments that are being sent, for example:

1. Write comment
2. Click to send it
3. Immediately switch tab

When switching the tab, the comment will be detected as "draft" but will be sent not long after. I think that there should be an event we can listen to so that when the comment is submitted, the label is removed.

I wonder how this can be solved easily and comprehensively (wait-for-ci for example also will cause this)

[cheap-glitch]

When switching the tab, the comment will be detected as "draft" but will be sent not long after. I think that there should be an event we can listen to so that when the comment is submitted, the label is removed.

We could try listening to the submit event of every form on the page.