Switch to OOP Hooks

Problem/Motivation

Module hooks added OOP support in D11.0. See https://www.drupal.org/node/3442349. While procedural hooks won't be removed in D12, it would still be a good idea to go ahead and make the switch now.

Proposed resolution

1. Create Drupal\oembed_providers\Hook\MediaSourceHooks and Drupal\oembed_providers\Hook\FormHooks classes.
2. Add BC code in oembed_providers.module and in oembed_providers.services.yml. See https://www.drupal.org/node/3442349#hook_convert.
3. Update oembed_providers.api.php.
4. Create Drupal\oembed_providers_test\Hook\OembedProvidersHooks class.
5. Add BC code to oembed_providers_test.module and in oembed_providers_test.services.yml.
6. Add [module_name].skip_procedural_hook_scan: true to oembed_providers.services.yml and to oembed_providers_test.services.yml.

Remaining tasks

1. Open MR
2. Verify tests pass

User interface changes

None

API changes

None

Data model changes

None