Xiang Zhang authored Jun 10, 2019 and David Flynn committed Nov 21, 2019

This adoption permits coding geometry with non-cubic bounding boxes.
Since the depth of the tree remains constant for cubic and non-cubic
bounding boxes with identical largest dimensions, quad-tree and
binary-tree partitions are introduced to avoid coding 'fractional'
positions.

The following configuration options control the placement of non-octree
partitions within the coding tree:

 --max_num_implicit_qtbt_before_ot
 --min_implicit_qtbt_size_log2

The geometry tree nodes contain a position element (pos) that identifies
the spatial position of the node.  At internal nodes this node position
is the partial position of a point and may either be represented using
the magnitude of the decoded points, or the magnitude of the current
depth.

The first form equates to:
 nextPos = curPos | (xyz << currentNodeSize)

The second:
 nextPos = (curPos << 1) | xyz

Where xyz represents a position bit from the coded occupancy.

In order to use the first form to determine neighbour relationships,
curPos must be shifted down to represent position within the current
depth.  This repeated shifting, along with the introduction of
simultaneous quantised and unquantised positions becomes increasingly
difficult to follow when adding non-cubic nodes (via OtQtBt).

This commit switches the representation to the second form above,
eliminating various shifted forms and duplicate state.  A decoded
positions is inverse quantised when reaching a leaf node.

This commit adds an extra contextualisation bit for occupancy coding
based on there being an unoccupied adjacent child neighbour, rather
than just depending upon the number of occupied neighbours.

This is part of a series attempting to remove unhelpful typedefs.

The commit adds a flag to conditionally enable/disable the feature.

Each occupancy bit is contextualised based on the number of occupied
(directly) adjacent child nodes in the (x-1), (y-1), and (z-1)
neighbour nodes used to generate the neighbour pattern.

Three contextualisation states are added:
 - no adjacent neighbours
 - one adjacent neigbour (=adjacencyGt0)
 - two adjacent neighoburs (=adjacencyGt1)

The neighbour pattern for a node indicates occupied neighbouring nodes.

This commit updates the definition of occupancy for the (x-1), (y-1),
and (z-1) neighbours to be occupied if the neighbour's adjoining
children (ie sharing a face with the current node) are occupied.

In the 1-D figure below, at a depth d, the node 'X' has two occupied
neighbours 'R' and 'L'.  When determining the neighbour pattern of X,
the (x-1) state of the neighbour's adjoining child ('r') is used
instead.  For completeness, nodes marked with '?' are not causally
available.

  d+0:   R|X|L
  d+1:  Rr|??|??

This commit removes unnecessary include directives.

The geometry coder is quite large, especially with trisoup and has no
benefit to being a header only implementation.  This commit moves the
geometry octree coder out of the header files and into
geometry_octree_{en,de}coder.cpp.