Add Dirt Slabs and related subtypes

[primetoxinz]

• [x] Dirt Slab
  • [x] Crafting 4 from 2 dirt.
• [x] Grass Slab
  • [x] Grass spreads to Dirt slabs
  • [x] Grass slabs spread to Dirt Blocks and Dirt Slabs
• [x] Dirt Path Slab
  • [x ] Clicking other slabs with shovel turns into Dirt Path Slab
  • Note: Dirt Paths cannot be created when Snow is on top, but since snow is a state on Slabs this is not the case for these.
• [x] Mycelium
  • [x ] Spreads from Mycelium Blocks or other Mycelium Slabs
  • [ x] Mycelium Slabs spread to Dirt Blocks.
• [x] Podzol Slabs
  • [x ] Mega Spruce growth chances dirt,mycelium and grass slabs to podzol slabs
• [x] Snow (as a blockstate)
  • All slabs (except path) accumulate snow when it is snowing.
  • Snow layer on slabs can be selected intentionally and removed.
  • Snow layers can be placed onto slabs
  • Light Level >11 melts snow off slabs and stops accumulation
• [x] Grass, Mycelium and Podzol slabs can be Skill touched

[RatherBeLunar]

Mycelium slab seems okay since it spreads like grass.

If you take on podzol, keep an eye on how some trees (I think 2x2 spruce?) convert some blocks into podzol below them. For consistency, it would probably good to allow some slabs to be converted to podzol as well. Maybe that's unnecessary, but it would feel better to me if it were supported for consistency.

[primetoxinz]

Copying my message from discord:

Almost forgot about this. Should we do the same kind of snow support? Where Snow precipitation logic will place the layer on the block above the slab but visibly move the render and collision box to the correct location in the slab?

Alternatively, could just make it a block state the occurs randomly during snow precipitation at a similar rate to normal blocks and handle when you mine the block in that state it only removes the snow.

First is lots of mixin' Second is more specific to our block and thus won't be an actual minecraft:snow