Migrating assets to a plugin causes references to break

The migrate function is meant for moving assets from one content folder to another, so it does no actual modification of the references in the migrated assets. This is normally fine, since we expect those references to be relative to /Game, the project's content folder. However, plugins may also have content folders, so we need to detect when something is migrated into a plugin and replace Game with the plugin name.

1. Create a texture named MyTexture and a material named MyMaterial in your content folder. Assign your texture to the material. Note that the texture path is listed as /Game/MyTexture.
2. Right click MyMaterial and migrate it to a plugin's content folder.
3. Open MyMaterial, and note that the texture reference still points to /Game/MyTexture instead of /PluginName/MyTexture.