UrlChooser should prefer to show files that are not under asset_imports when hiding duplicates

If the same file is found from asset_imports and under content, the one under content is likely that one user wants to use, so when we are hiding duplicates in UrlChooser, prefer to hide the files under asset_imports rather than just showing the first instance we come across.

This is important because e.g. effect composer can create duplicates of image assets under asset_imports and those can be also removed by effect composer at any time, breaking any Image element that might have used the same asset.