Provide Block Pattern for Widget + Title to streamline creation of previous Widget screen markup

[getdave]

What problem does this address?

As discussed at length in #32723 the previous (non-block based) Widgets screen provided a discrete HTML structure for a "Widget".

This was:

• Wrapping container element (Widget wrapper)
• Heading element (Widget title)
• Widget (the actual body of the Widget itself).

The new block based editor doesn't do this. Instead each block that is added is treated as a standalone "Widget". This makes is very difficult to replicate the structure of the previous Widgets screen in the new screen. This is often necessary for reasons of backwards compatibility.

What is your proposed solution?

I've been exploring providing a Block Pattern called "Widget and title". When added this creates:

• core/group block with a class of c-widget.
• [Child] core/heading block with a placeholder and a class of c-widget__title.

All the user then need do is insert their chosen widget block (e.g. Archives) as a sibling of the Heading block (child of the Group) and you have a good replica of the previous structure.

This avoids the hassle of creating it manually. Here's a demo of a prototype I created by hardcoding some block patterns in the edit-widgets package:

Screen.Capture.on.2021-08-04.at.13-39-42.mp4

In the future we could also explore whether it's possible to automatically transform a standalone Widget block into this Pattern.

[justintadlock]

Related: #26170

[draganescu]

This has been solved by the introduction of the Widget Group block.