Disabled conditions for publish buttons

[oandregal]

We have two components that can be used to publish a post: PostPublishToggle or PostPublishPanelButton. The first will open the PostPublishPanel sidebar, the second is used in the PostPublishPanel sidebar, and substitutes the toggle when pre-publish checks are disabled or when the post is published.

The conditions under which they are disabled are different at the moment, tests pass due to wrong assumptions and/or conditions aren't met. In bold what this PR fixes:

	Button	Toggle
isSavingPost=true	disabled	disabled
forceIsSaving=true	disabled	disabled
isEditedPostSaveable=false	disabled	disabled
isEditedPostPublishable=false && forceIsDirty=false	disabled	disabled
isCurrentPostPublished=true	-	disabled
isPostSavingLocked=true	disabled	-
isEditedPostSaveable=true && isEditedPostPublishable=false && forceIsDirty=true	enabled	enabled
isEditedPostSaveable=true && isEditedPostPublishable=true && forceIsDirty=false	enabled	enabled

Testing

Button and Toggle are disabled while a draft is being saved

• Create a new post.
• Click "Save draft" button.
• Check that publish toggle is disabled.
• Repeat for the publish button (disable pre-publish checks in "More options > Options" modal first).

They should look like this:

Note that when a post is being published, the button should show a busy status instead:

Button and Toggle are disabled when forceIsSaving is true

• Create a new post.
• Open the console and execute wp.data.dispatch( 'core/edit-post' ).requestMetaBoxUpdates();
• Check that the publish toggle is disabled for a quick moment.
• Repeat for the publish button (disable pre-publish checks in "More options > Options" modal first).

They should look like this:

Toggle is disabled if post is published

No manual testing for this, we have a unit test that covers it. In Gutenberg case, the toggle is never shown if the post is published (we show the button instead). TLDR: at this point in the release cycle I don't want to introduce API changes.

Toggle is enabled if post is saveable (has contents) and forceIsDirty

No manual test for this either. Same reasons than above. Note that forceIsDirty has been added here as a new condition just for completeness. It doesn't modifies API.

[oandregal]

@tofumatt this is part of figuring out the accessibility stuff. I'm trying to merge this two buttons, which implies I need to understand (and fix!) their enable/disable states.

[tofumatt]

Worked for me! The manual testing instructions here read like they'd make good E2E tests 😏