Fix custom status error with Gutenberg 7.2+

[cojennin]

A fix for #583. Continuing to break the rules, but for a good cause.

Props to @ryelle for tracking this down

Steps to Test

1. With Gutenberg 7.2 or 7.3
2. With the custom status module active
3. Try to edit a draft post
4. Editor should not crash

[ryelle]

Loading, editing, and saving a draft works, but after the draft finishes saving, the button reverts to "save draft"

I'm also seeing a crash with a custom status ("assigned")— this time, the post loads fine, but crashes when I try to save it. The error is the same:

Error: Failed to execute 'removeChild' on 'Node': The node to be removed is not a child of this node.

[WPprodigy]

I can replicate the above as well.

Seems GB is changing the markup pretty drastically during the saving states. Perhaps utilizing more of the selectors could help here, like select( 'core/editor' ).isSavingPost(). Also, subscribe() isn't re-triggered when saving is done, that's why it ends up in the "save draft" state at the end still.

Also noting that WordPress/gutenberg#12517 (filtering text strings) is another issue to watch as a better way to solve this.

I'll see what I can find/do later this evening.

Edit: Ugh, and there is also WordPress/gutenberg#17632 (fire hook when post is finished saving) that would help here (was closed in favor of WordPress/gutenberg#13413, though it is a bit different IMO).

[WPprodigy]

Tried a different approach in #585

[cojennin]

Closing in favor of #585