[iOS VMD Flow] Change how we handle image error

[hugolefrancois]

Description

The current way to know if an VMDImage "remote" image has failed to load wasn't working. The .placeholder modifier is not triggered again when the @State of the VMDImage changed. To fix that, I have use an environment variable to expose that stat outside of the VMDImage. That environment variable is then accessible in the placeholder view.

Unfortunately, I have to make a breaking change to remove the .placeholder modifier with the param that is not working and I also had to remove the "empty" value of the LoadingStatus enum because this state wasn't really possible.

How Has This Been Tested?

On my project and in Sample app

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)