Block Bindings: Map edit_block_binding capability

[SantosGuillamot]

What?

This pull requests add compatibility to create a edit_block_binding capability that will be mapped to what was decided here.

Why?

The compatibility filters should work the same way as core.

How?

Adding a new edit_block_binding capability through an init hook.

Testing Instructions

1. Register some meta fields in your site.

	register_meta(
		'post',
		'my_custom_field',
		array(
			'show_in_rest'      => true,
			'single'            => true,
			'type'              => 'string',
			'default'           => 'Default',
			'revisions_enabled' => true,
		)
	);

2. Go to a page as an admin and check you can connect a paragraph to the custom field.
3. Insert a filter to modify the manage_block_bindings capability and disable it:

function restrict_edit_block_binding_cap( $caps, $cap ) {
	if ( 'edit_block_binding' === $cap ) {
		return array( 'do_not_allow' );
	}
	return $caps;
}

add_filter( 'map_meta_cap', 'restrict_edit_block_binding_cap', 10, 4 );

4. Go to the page and check you can't create the connections anymore.

[SantosGuillamot]

Using empty was wrong because it could be false and that is a valid value. This means we were overriding the setting from core even if it was defined there.

[SantosGuillamot]

Migrating the code triggered a bug where the attributes panel is not shown in custom post types when Gutenberg plugin is not active. This is because the mapping capabilities logic wasn't correct. e2e tests passed because that logic was being overridden in Gutenberg.

I've started a PR in core trying to address that: link.

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Co-authored-by: SantosGuillamot <santosguillamot@git.wordpress.org>

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