Make issue/PR body visible while the rest of the conversation is still loading

[Fs00]

This PR mitigates the sometimes very slow loading of issue/PR conversations (due to GH REST API limitations we all know) by showing the issue/PR body as soon as possible, instead of waiting for the rest of the conversation to load.
This can be best demonstrated by the screencast here: https://streamable.com/aj4p28.

This way, the user can start reading the content of the issue/PR without waiting, drastically reducing the perception of the loading times.
The only thing I'm not too sure about is whether we should keep the editor bottom sheet hidden while loading is in progress. There is technically nothing that can prevent us not to show it, but at the same time it doesn't make much sense to use it before the conversation is loaded.

Note: I've tried to workaround some issues with the editor bottom sheet that are also present in the current version of the app. Some glitches are still present when rotating the screen, but I haven't had enough time to understand how bottom sheet positioning/resizing works in order to do a proper fix and I'm not sure whether I want to. 🙂

A sidenote: I personally think that we shouldn't expand automatically the list of check runs when there are some failed checks. As you can see in the screencast above, for repositories that have something like 20+ checks (PowerShell/PowerShell and dotnet/runtime are great examples) it becomes a bit annoying having to scroll down the list to reach the first comment (yes, you could collapse it but often just happens to go brainlessly straight to the conversation 😅).

[maniac103]

This sounds like a good idea. From looking at your screencast, a few things don't yet seem ideal to me:

• Do checks have a relevant loading time? The checks row 'popping into place' seems a bit weird to me. Should probably have a loading placeholder for those.
• 👍 for not auto-expanding checks based on that PowerShell PR
• Keeping top progress bar active seems a bit redundant to the comments loading indicator, I think the latter is sufficient

The only thing I'm not too sure about is whether we should keep the editor bottom sheet hidden while loading is in progress. There is technically nothing that can prevent us not to show it, but at the same time it doesn't make much sense to use it before the conversation is loaded.

Indeed, I'd also say to only show it when loading is done.

[Fs00]

Do checks have a relevant loading time?

Sometimes yes, and in these cases the pop-in effect can be seen in the current version of the app too, if the conversation loads fast enough.
This pop-in would surely be noticed more often after this change, so I agree on the placeholder👍

[Fs00]

• Do checks have a relevant loading time? The checks row 'popping into place' seems a bit weird to me. Should probably have a loading placeholder for those.
• +1 for not auto-expanding checks based on that PowerShell PR

Done, give it a try :)

Keeping top progress bar active seems a bit redundant to the comments loading indicator, I think the latter is sufficient

After experimenting a bit, I don't really agree on this. In case you have a long issue/PR body so that the comments loading indicator can't be seen without scrolling down, the top progress bar makes it clear why the comment editor is still kept hidden.
Otherwise, the feeling you get without scrolling down is that everything is loaded, but then suddenly the comment editor pops up without any apparent reason. I find it a potentially surprising/confusing behavior.

[Fs00]

I've pushed a fix and one more tweak, I think this can be considered ready.

[Fs00]

Fixed conflicts and rebased.