EmbedCodeFactory::getSelectOptions performance improvements

Problem/Motivation

Everytime \Drupal\acquia_dam\EmbedCodeFactory::getSelectOptions is called, the allowed image styles are calculated, even if the asset type is not image.

It also recalculates the thumbnail option on each call.

Steps to reproduce

\Drupal\acquia_dam\Plugin\CKEditor5Plugin\MediaEmbedCode::getDynamicPluginConfig calls \Drupal\acquia_dam\EmbedCodeFactory::getSelectOptions multiple times.

Proposed resolution

1. Only populate `image` if asset type is null or image
2. Statically cache the results for future calls in the same request

Remaining tasks

User interface changes

API changes

Data model changes