Get or set the AssetBundle variant.
This property has a value when the Asset is assigned to a specific variant of an AssetBundle, and corresponds to the second dropdown of the AssetBundle control found at the bottom of the Inspector.
Its value is stored in the .meta file for the Asset, and inside the AssetDatabase.
This property is not used when AssetBundles are being built programmatically with the signature of BuildPipeline.BuildAssetBundles that accepts an array of AssetBundleBuild structures.
Additional resources: AssetImporter.assetBundleName, AssetBundleBuild.assetBundleVariant