MC-8187 / 2x2 Surrounded Saplings Fix

The 2x2 Surrounding Saplings fix for MC-8187 allows 2x2 saplings such as spruce,
jungle and dark oak to grow even when completely surrounded on all 4 sides.

How does it work?

Simple, it fixes an offset in TreeFeature.getTopPosition that makes 2x2 trees
check a 3x3 area at the trunk, catching additional blocks that don't determine
how the tree should grow.

How do I use it?

Simply install Fabric or Quilt for Minecraft 1.16 and newer,
then install this mod.

Any side effects?

Theoretically, 2x2 trees may spawn more frequently in a given world,
and old builds not expecting 2x2 saplings to grow may suddenly get a surprise.

Any modded trees that are 3x3 may also erroneously check for a 2x2 trunk if it
relies on the generator to filter out whether a space is valid.

Fun facts:

• This mod was written on 1.16.5 and works as is on 1.16 through 1.20.1.
• I wrote this mod using Segoe Script.
• Some hate the compatibility cockroach that is this mod.