Support texture name objects with side keys, in addition to arrays

Now all formats from https://github.com/deathcap/cube-side-array are
supported - including strings (one texture for all sides), arrays
(of various lengths for various sides), and objects (with keys named
after the sides). https://github.com/deathcap/voxel-pumpkin uses the
latter, so this fixes https://github.com/deathcap/voxel-inventory-crafting
viewing the 'plants' section, which used to crash with an invalid
texture name (now caught in deathcap/artpacks@e995ff6e838cec8cb36c386928ffce46a374099f).
Remove deprecated getPackedBlockIndex
0.8.0