Block variation transforms with InnerBlocks and custom transforms

[ntsekouras]

The problem that needs solving here is having a way to 'update' a block to another block variation, after its creation.

The first step was to handle the 'simple' block variations, and by 'simple' I mean the variations that were applying specific attribute values only. In this step the feature was introduced to Navigation block. (issue: #25231, PR: #26687)

Now we need to implement a way of handling all block variation transforms. This means we have to handle blocks with InnerBlocks as well, like Query, Columns etc..

Another thing is that there will be a need for extending variations API to support custom transforms. For example changing a Columns block of 3 columns to 2 columns. This might be a separate issue and step 3 of this problem though...

Block variations reference: https://developer.wordpress.org/block-editor/developers/block-api/block-registration/#variations-optional

[mapk]

Aligning with the Navigation block, I imagine the Query block would look similar to this:

There's some oddly repeated description text for each of these options though. It will most likely need a copy review.

[mapk]

Here's how this would look without descriptions.