First build of 21.9 Phase 2 Upgrade release branch. Supports Pixel TDR/"step 2.2" geometry (ATLAS-P2-ITK-20-00-00/ATLAS-P2-ITK-20-03-00) but this geometry and reconstruction output are not guaranteed to be completely frozen, and small changes are to be expected due to changes to e.g. passive material descriptions. Support for newer layout versions (LTF2/"step 3.0") will follow in future releases.