[MC-62552] FallingSand shows alternate block textures while falling

Fix note

Now the block remembers its 'shape' when it started falling. When it lands it will take the final shape it will get as if it was placed there.

The bug

When FallingSand falls, it changes its texture for every block position it passes instead of using the texture from the block where it started and then only changing it once it landed.

How to reproduce

Use the following command to summon FallingSand above you and watch it fall

/summon FallingSand ~ ~20 ~ {Time:1b}