Overworld and Nether y coordinate changes

Shift the y coordinates in the overworld to be nonnegative, and the y coordinates in the nether to be nonpositive.

The new overworld would shift to y = (0,384) and new nether coords would be y = (-256,0) with 0 in both cases being the bedrock layer. Additionally, because the build height is changed, the sea level should be shifted upwards to y=110 (equivalent to y=46 in older versions), putting the sea level at about 30% build height limit.

This would allow for sharing coordinates to be easier, as seeing a negative y coordinate automatically tells the player that the coordinate is in the Nether. (and positive guarantees it's in the overworld).

I know that lorewise the Nether is not directly below the overworld, and this might confuse some people on that side of the community, but I think this is too useful to look over for solely that reason.