Update TinyMCE to no longer strip <picture>, <source> tags

[Casey_Grimes]

When developing email templates that work with both light and dark mode, using <picture> and <source> tags with a fallback <img> inside it is a clean way to set both light and dark mode images without having to assign the image a conditional media query show/hide via CSS. However, the TinyMCE editor today will strip this markup rather than allow it to be in editable areas. Can this please be updated to no longer have this behavior?

[DeepthiA]

Hi @caseyw 

We invite you to try our new email designer, which has a dark mode email editing experience to enable you to define dark mode styling in a dark mode native editor. This is slightly different from the Marketo v2 email template authoring experience where it was HTML only. Here in the new designer we encourage users to design their email templates in a visual no-code interface and are continually releasing new features to enhance the experience.

Here is a documentation on how to achieve dark mode email editing: https://experienceleague.adobe.com/en/docs/marketo/using/product-docs/email-marketing/email-designer...