WYSIWYG editor not saving inline images for advanced html/text editor.

Problem/Motivation

When uploading an image through the WYSIWYG editor in the Advanced HTML/Text editor, the image is not saved as a drupal managed file. The image itself does upload at the time to sites/default/inline-images, however, coming back a day later the image has been deleted resulting in a 404.

Steps to reproduce

1. Create new form and add an Advanced HTML/Text editor element
2. Upload an image through the WYSIWYG editor
3. View the form and confirm your image is there
4. At this point, not sure how or when the deletion gets triggered, but the image is deleted from the sites/default/inline-images directory resulting in a 404. This happened twice to me in 48 hours. I thought running cron would trigger the deletion but it didn't.

Proposed resolution

I think when uploading the image, the image needs to be saved using file_save_data or file_save_upload and then using the 'file.usage' service to register the usage of the file which will automatically mark it as permanent.