Merge Tags stripped from Background Image setting instead of processing

[jakejackson1]

Description When using the Background Image feature with a merge tag in the value, it is automatically stripped out when output in the PDF via esc_raw_url().

Step To Reproduce Steps to reproduce the behavior:

1. Setup a Core PDF on the form
2. In the Background Image setting insert a URL to an image in the media library
3. Add a merge tag to the image URL
4. View the PDF and append URL with ?html=1
5. View the page source and see the merge tag was not correctly converted to the associated value

Expected behavior Merge tags should be processed correctly. Because we need to escape on output, merge tags should be pre-processed for this particular field setting.

[jakejackson1]

Notify HS issues with tag background-image-tags upon fix