Block Bindings: block doesn't receive full __default bindings during render

[talldanwp]

Original gutenberg issue - ​https://github.com/WordPress/gutenberg/issues/64688

TLDR - some image block features don't work correctly when the image is using a pattern override due to some missing block bindings code in core.

---

Longer explanation:

The pattern overrides feature is built upon block bindings, and uses a special __default binding that means all block attributes that support binding are bound:

bindings: {
    __default: 'core/pattern-overrides'
}

During processing of the bindings, this single __default binding is replaced with the individual binding attributes - e.g.:

bindings: {
    src: 'core/pattern-overrides',
    id: 'core/pattern-overrides',
    caption: 'core/pattern-overrides',
}

In the gutenberg plugin this updated bindings metadata is assigned back to the block before rendering so that the block can reason about which individual attributes are bound:
​https://github.com/WordPress/gutenberg/blob/98b8d415830fa9ebf7b4b0a2b95d65b9fd1e813a/lib/compat/wordpress-6.6/blocks.php#L40

This allows blocks like the image block to check whether an individual attribute, like id, has a binding:
​https://github.com/WordPress/gutenberg/blob/98b8d415830fa9ebf7b4b0a2b95d65b9fd1e813a/packages/block-library/src/image/index.php#L31

Unfortunately, WordPress core doesn't have the same logic to assign the updated binding metadata back to the block before rendering, which means the image block's logic fails. The block only receives the individual default binding in its metadata.

Trac ticket: https://core.trac.wordpress.org/ticket/62069
Gutenberg issue: ​https://github.com/WordPress/gutenberg/issues/64688

## What
Fixes an issue with the image block when using pattern overrides caused by a bug in the block binding logic.

## Why does the bug happen?
The pattern overrides feature is built upon block bindings, and uses a special default binding that means all block attributes that support binding are bound:

bindings: {
    __default: 'core/pattern-overrides'
}

During processing of the bindings, this single default binding is replaced with the individual binding attributes - e.g.:

bindings: {
    src: 'core/pattern-overrides',
    id: 'core/pattern-overrides',
    caption: 'core/pattern-overrides',
}

In the gutenberg plugin these individual bindings are assigned back to the block before rendering so that the block can reason about which individual attributes are bound:
​https://github.com/WordPress/gutenberg/blob/98b8d415830fa9ebf7b4b0a2b95d65b9fd1e813a/lib/compat/wordpress-6.6/blocks.php#L40

This allows blocks like the image block to check whether an individual attribute, like id, has a binding:
​https://github.com/WordPress/gutenberg/blob/98b8d415830fa9ebf7b4b0a2b95d65b9fd1e813a/packages/block-library/src/image/index.php#L31

Unfortunately core doesn't have the same logic to assign the individual bindings back to the block before rendering, which means the image block's logic fails. Any block that renders just receives the individual __default binding.

## How has it been fixed?
The fix in this PR is to ensure that the process_block_bindings method returns any updates to the block's binding metadata along with other computed attributes.

Prior to rendering, the block's attributes are updated with the result of this method (it's where the binding attribute values are updated for a block):
​https://github.com/WordPress/wordpress-develop/blob/d8e05446b7d109f8b3c48cbeebf6241d3f6e3946/src/wp-includes/class-wp-block.php#L465-L470

So this will achieve the same result as the code in the Gutenberg plugin.

There are two failing e2e tests, but they also seem to be failing in trunk.

That makes perfect sense to update the metadata.bindings for the __default special case together with computed values for attributes 👍🏻

[cbravobernal]

In 59095:

Block bindings: Ensure block receives default bindings when render.

Fixes an issue with the image block when using pattern overrides, where the image block with overrides enabled was not outputting all the expected image attributes. Ensures that the process_block_bindings method returns any updates to the block's binding metadata along with other computed attributes.

Props talldanwp, cbravobernal, santosguillamot, mukesh27, gziolo.

Fixes #62069.

Committed with https://core.trac.wordpress.org/changeset/59095