Switch HIGG3DX to multiple BTagging training containers for ATLASDPD-1334
This MR makes the necessary updates to the HIGG3DX derivation formats in order to use the newly implemented multiple BTagging training containers (and associated jet shallow-copy containers).
Discussion on the required updates in ATLASDPD-1334. These changes should fix the ART tests for the HIGG3D1 / HIGG3D3 formats.