Use PHP attributes instead of doctrine annotations

Problem/Motivation

We use Doctrine's annotations to add metadata to our classes. For example, Block's use annotations to set the block ID and admin label. PHP 8.0 introduced a new language feature PHP attributes to support such metadata.

Proposed resolution

• Add support for PHP attributes
• Deprecate doctrine annotations for removal in Drupal 11.

Here's an example of a block annotation:

/**
 * @Block(
 *   id = "system_powered_by_block",
 *   admin_label = @Translation("Powered by Drupal")
 * )
 */
class SystemPoweredByBlock extends BlockBase {
  // ...
}

PHP attributes options

Use named arguments

#[Block(
  id: "system_powered_by_block",
  admin_label: "Powered by Drupal"
)]
class SystemPoweredByBlock extends BlockBase {
  // ...
}

Use arrays

#[Block(array(
  "id" => "system_powered_by_block",
  "admin_label" => "Powered by Drupal",
))]
class SystemPoweredByBlock extends BlockBase {
  // ...
}

Use individual attributes

[#BlockId("system_powered_by_block")]
[#BlockAdminLabel("Powered by Drupal")]
class SystemPoweredByBlock extends BlockBase {
  // ...
}

Problems to solve

• How to support @translation. Nested attribute support was only added in PHP 8.1 - see https://wiki.php.net/rfc/new_in_initializers#nested_attributes
• The unused use sniff we use is problematic - need to move to slevomatic version - #3010032: Add dependency on slevomat/coding-standard

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet