FSE: Header template part has extraneous UI for group block

[shaunandrews]

Our current Header template part uses a Group block to contain all the elements in the Header.

This adds an extra click to edit anything in the Header, which creates some confusion. Also, the settings for the Group block allow a customer to add a background color which "breaks" the design.

There's also the ability to add a new block outside of this group using the default inserter.

Doing so will break the layout of the site.

I suggest we remove the ability to interact with the parent Group block. That is, a customer should not be able to focus the Group block, nor update its settings in the sidebar. There's also an extra inserter button that appears at the bottom-left of the Group block — we should also remove this.

Similar, we should remove the ability to add blocks outside of this Group block.

[shaunandrews]

Turns out once you interact with that inserter below the Group block its impossible to remove it. I now have an empty placeholder in my site's header:

[gwwar]

I suggest we remove the ability to interact with the parent Group block.

This likely needs to be specific to the theme/header content. Folks may want to look into the Gutenberg template block API, where we can lock down specific elements.

https://developer.wordpress.org/block-editor/developers/block-api/block-templates/#locking

How blocking is this @shaunandrews ?

[apeatling]

The only reason we need the group block is to apply the css classes that the theme needs. If we can find a way to apply the class names without the group block, that might be the easiest direction.

[shaunandrews]

Here's a related Gute issue mentioning the need for this same functionality: WordPress/gutenberg#7469