Fix webapi product custom attribute preprocessor execution

[gustavosolomon]

Description

This fixes the issue related to Webapi product custom attribute preprocessors described in the following issue:

#38633

Basically this fixes the validation mechanism that checks which preprocessor should run.

This also updates some function names and interface parameters, which is related to the issue fix.

Fixed Issues

1. Fixes [Issue] Webapi product custom attribute preprocessor #38633

Manual testing scenarios

1. Inject an processor object, using "customAttributePreprocessors" array in ServiceInputProcessor class.
2. The processor injected to "customAttributePreprocessors" array should implement PreprocessorInterface interface. (Example bellow)
3. Clear cache / generated code.
4. Send a POST request to product API endpoint, in order to create/update some product data.
5. Include manufacturer value inside custom_attributes data
6. Processor process function should execute the desired code. (IE: die('manufacturer: it works');

<?php

declare(strict_types=1);

namespace Vendor\Module\Webapi\CustomAttribute;

use Magento\Framework\Webapi\CustomAttribute\PreprocessorInterface;

class TestProcessor implements PreprocessorInterface
{
    public function shouldBeProcessed(string $key, $attribute): bool
    {
        return true;
    }

    public function process(string $key, &$attribute)
    {
        // Do something with the attribute
        die('manufacturer: Do something with the attribute here');
    }

    public function getAffectedAttributes(): array
    {
        return ['manufacturer'];
    }
}

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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[gustavosolomon]

@magento run all tests