fix: add checkerboard bg behind images so that transparent pixels are visible

[shsteimer]

Description

When an image with a transparent bg is added, they can be hard to see in the editor window. This adds a checker board pattern behind all images, to make those easier to see

Related Issue

Originally created #1093 but tests failed due to branch name length.

Motivation and Context

How Has This Been Tested?

tested locally

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

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Commits

• 768d2b9 ✅ (latest)
• 83162dc ❌