Function to process arguments passed to the main methods in the
cdid package to compute ATT from deltaATT. For more details on the methodology, see:
Bellego, Benatia, and Dortet-Bernadet (2024), "The Chained Difference-in-Differences",
Journal of Econometrics, https://doi.org/10.1016/j.jeconom.2023.11.002.
gmm_convert_delta_to_att(dp)a DIDparams object
a dp object