The method "PrefabLoader::GetRelativePathToProject" has been changed to "PrefabLoader::GenerateRelativePath", and reworked to get a correct relative path. GetFullPath has also been modified to get correct relative paths too. This requires an Asset Processor connection - if one isn't available (like during unit tests), the methods have fallback logic to produce project-relative paths.
With this change, SliceConverter can't use SaveTemplate() to save the file any more, because GetFullPath now expects to find an existing path, which doesn't work for not-yet-created files. Instead, it now has to use the same technique as the Editor and call SaveTemplateToString then save the string out as a file.
Nested slices are now detected, converted into prefabs, and the top-level prefab will get linked to the nested prefabs with the proper number of instances. However, the nested prefabs won't retain any of the slice override values or parent entity hierarchy. That will (hopefully) be added in a separate PR.
This also adds support for better relative source paths for nested prefabs. To support this, the tool now needs to connect/disconnect with the AssetProcessor to be able to turn a slice asset ID into a relative source path, so that nested templates can be looked up and converted correctly.
Mike Balfour
Chris Galvan