Assets with required extensions should log a warning

I recently encountered some files that don't work in certain viewers due to required extensions in the asset. I wonder if it makes sense to put a warning in the report when this happens? We show that there is a required extension, but everything appears green and so people expect them to work everywhere.

No file, test, or entry point is named. Start by tracing how required extensions are represented in the report and locating the existing report checks and tests; done means affected assets visibly produce a warning rather than appearing entirely successful.

Written by the indexing model from the issue text.