Investigate validation bug allowing theme files to reference files from a different theme

[pakim1]

Description and Context

There was an issue that a theme installation was getting stuck in-progress which was reported by a customer. The root cause of this issue was tracked down to a metadata file from a module in the downloaded theme that was referencing a CSS file and image from a different theme from the provider. While fixing the references resolved the customer's issue, this should've been caught by the validation logic as an error before the provider was able to list the theme on the marketplace so should be fixed or added to the validation logic if it's not there.

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