Native block reflection/rotation

[jedediah]

• Vec3 base interface for all vectors (replaces BlockPosition). Unifies "fine" (double) and "coarse" (integer) vectors, and provides a rich API thanks to Java 8 interface methods. MutableVec3 subtype provides mutation. VectorFactory service is used for construction i.e. Bukkit.vectors().
• Transform interface representing spatial transforms, and CoarseTransform subtype for block transforms.
• BlockRegion interface that extends Set<Vec3> and represents a set of block positions, which can be transformed, filtered, and "baked" (made immutable). CuboidBlockRegion is the only shape provided currently.
• Expanded BlockImage that supports transforms and reading individual blocks as MaterialDatas (eventually it will also provide BlockStates, but that is tricky due to how they are constructed).
• BlockReflection and BlockRotation enums reflecting the ones Mojang uses for structure blocks, and a BlockRotoflection class that combines them. These can all be converted to CoarseTransforms.
• BlockFactory service to apply reflection and rotation to MaterialData for blocks (through the native API).
• Various enhancements to BlockFace to support reorientation.
• An Axis enum with values X, Y, Z
• Lots of tests
• Removed ImBlockVector because BlockVector semantics are pretty sketchy and caused problems. Recommend using a coarse Vec3 instead.
• Location no longer extends Vector, also due to sketchy semantics, but it does contain a Vector that can be accessed directly (and mutated) through Location#position().

Breaking changes:

If you use any SportBukkit-specific features related to vectors/regions/images then this will probably break a lot. This was necessary to get all the power we wanted out of the API. Bukkit-compatible code should not break at all.

[jedediah]

Updated description. Going to merge this now so it's out of the way when we rebase to 1.11