Changes in Z coordinate normalization in 3D landmarks

• TfLiteTensorsToLandmarksCalculator
  • It now always normalizes Z coordinates by image width (as for X) when producing NORM_LANDMARKS output, assuming a weak perspective projection camera model.
  • The normalize_z option can be used to further normalize Z coordinates by an additional factor. For instance, normalize_z: 0.4 is now used in hand tracking to better account for the Z coordinate distribution in the training data.
• Bug fixes
  • Fixes issues on Ubuntu 20.04, resolving #820.
• Documentation update
  • Added instructions for building for Nvidia Jetson and Raspberry Pi devices with ARM Ubuntu.