Manually set IncomingDirections for neighbor chunks during searching

[Noryea]

This commit should make fewer chunks be loaded (the number approximately equals to 0.4.x)

[jellysquid3]

Why? This just reintroduces the bug we fixed with #1898. You are resetting the incoming directions for a chunk every time it is enqueued, but that breaks occlusion culling.

[jellysquid3]

To explain: Each chunk stores visibility information which describes which outgoing faces are visible for a given set of incoming faces. When performing the search, we can encounter a situation where the same chunk is traversed into multiple times from different directions. We use VisibilityEncoding.getOutgoingDirections to create a bit-field union of the outgoing directions over the input set of incoming directions.

[Noryea]

To be frank, I expected you to ignore this pull request(or close it without explaination), because it wasn't reasonable.
I did it just for a friend of mine, who uses a laptop with Intel HD Graphics 6000 and gets a lower framerate on servers after installing Sodium 0.5.0...

Thank you for explaining the details, sorry to bother you