Replace check_markup() and image_style_options(), deprecated in Drupal 11.4

Problem/Motivation

Drupal 11.4 deprecates two functions this module calls, and both are removed in Drupal 13. The phpstan job on 3.x reports them on every pipeline:

• image_style_options() in src/Plugin/Field/FieldFormatter/Thumbnail.php, which builds the image style list of the Thumbnail formatter settings. See the change record: use ImageDerivativeUtilities::styleOptions() instead.
• check_markup() in modules/video_embed_wysiwyg/tests/src/Kernel/FilterTest.php, which filters the test content. See the change record: there is no direct replacement, render a processed_text element instead.

The phpstan job is allowed to fail, so the pipeline badge stays green and hides both.

Steps to reproduce

Open the phpstan job of any 3.x pipeline, for example on !124: "Found 2 errors", both function.deprecated.

Proposed resolution

• Thumbnail formatter: the module still supports Drupal 10.3, where ImageDerivativeUtilities does not exist, so call it through DeprecationHelper::backwardsCompatibleCall() with image_style_options() as the fallback for core before 11.4.
• FilterTest: render ['#type' => 'processed_text', '#text' => $content, '#format' => 'test_format'] with renderInIsolation(), available since Drupal 10.3.

Remaining tasks

• MR
• Review

User interface changes

None.

API changes

None.

Data model changes

None.

AI-Generated: Yes (Claude Code was used to help draft this issue summary. I reviewed it before posting.)