Returns true if the current project was created as a temporary project.
A temporary project is one that was created using the "-temporary" command line argument. It is located in a temporary location in the filesystem (e.g. the user's TEMP or TMPDIR folder), and when closing the project the user will be prompted to select a permanent location for the project that it will be moved to.
Additional resources: EditorApplication.SetTemporaryProjectKeepPath.