[BetterPhpDocParser] Keep import used only in an annotation array key

[TomasVotruba]

Fixes wrong removal of a use import that is referenced only in the key side of a Doctrine annotation array, e.g. @ORM\DiscriminatorMap({ SomeEnum::TOTP = ... }).

Reported via demo: https://getrector.com/demo/a835e33e-668f-47f5-8cf8-604988f8b0de

Problem

ArrayItemClassNameDecorator resolved the class name only from the array item value ($node->value). A class used solely in the key (SomeEnum::TOTP) got no RESOLVED_CLASS, so getArrayItemNodeClassNames() never reported it. With removeUnusedImports() on, UnusedImportRemovingPostRector then treated the import as unused and removed it.

Before:

use Doctrine\ORM\Mapping as ORM;
use App\Enum\SomeEnum; // <- wrongly removed

/**
 * @ORM\DiscriminatorMap({
 *     SomeEnum::TOTP = "totp"
 * })
 */
class Foo {}

Fix

• Resolve a class from the key side too, stored under a new RESOLVED_KEY_CLASS attribute.
• getArrayItemNodeClassNames() now collects both value and key resolved classes.

Covered by a skip fixture in tests/Issues/NamespacedUseAutoImport.