Editor: Add ifPostTypeSupports higher-order component (try conditional render HoC pattern)

[aduth]

This pull request seeks to implement a new ifPostTypeSupports higher-order component which serves in place of the existing PostTypeSupportCheck and attempts to explore a new generalized pattern for conditional component rendering.

Example Before:

function MyFeaturedImage() {
	return (
		<PostTypeSupportCheck supportKeys="thumbnail">
			<img />
		</PostTypeSupportCheck>
	);
}

export default connect( /* ... */ )( MyFeaturedImage );

Example After:

function MyFeaturedImage() {
	return <img />;
}

export default compose( [
	ifPostTypeSupports( 'thumbnail' ),
	connect( /* ... */ ),
] )( MyFeaturedImage );

Implementation notes:

The thinking behind the naming convention is that we could create higher-order component-libraries with the following expectations:

Name	Behavior
ifSomeCondition	Renders component only if condition applies
withSomeProps	Renders component with additional props

Testing instructions:

Verify that there are no regressions in the behavior of post-type-conditional elements:

• Discussion (comments or trackbacks supports)
• Featured image (thumbnail support)
• Excerpt (excerpt support)
• Post format (post-formats support)
• Author (author support)
• Order (page-attributes support)
• Last Revision (revisions support)

[gziolo]

@jorgefilipecosta opened a similar PR. See #4812. In general both implementation are similar 😃

[aduth]

Well then... 😅

I think we could probably combine the two branches:

• Take README.md and completed replacement of PostTypeSupportsCheck from mine...
• ...and withConditionalRender (good idea!) and tests from @jorgefilipecosta 's

Can take a look tomorrow, or if @jorgefilipecosta wants to go ahead, by all means.

[jorgefilipecosta]

Thank you @aduth, I will merge both PR's 👍

[gziolo]

Thank you @aduth, I will merge both PR's

Yes, that would be nice. This one answers also some questions I had in the other PR :)

[aduth]

Closing in favor of #4812.