Introduced Anisotropic Surfacing Kernels and PCA methods

[Idclip]

New:
    - Introduced anisotropic surfacing tools in points/PointRasterizeSDF.h
    and principal component analysis (PCA) methods in points/PrincipalComponentAnalysis.h.
    The latter tool analyses point neighborhoods and computes affine
    transformations representing elliptical distributions. The prior tool
    takes rotational and stretch point attributes (optionally computed from
    the prior PCA methods) and generates anisotropic surfaces.

API Changes:
    - Re-worked the API in PointRasterizeSDF.h with the addition of anisotropic
    surfacing kernels. The new API exposes more concise free functions which
    take structs of parameters. The old API remains supported but is
    deprecated.

Improvements:
    - Improved the performance of PointRasterizeSDF.h tools with larger radii
    with better bound computation approximations.

Fixes:
    - Fixed a bug in points::rasterizeSpheres and points::rasterizeSmoothSpheres
    which could cause sections of the generated surface to incorrectly be marked
    as negative interior values.
    - Fixed a bug in points::rasterizeSmoothSpheres which could result in
    incomplete surface reconstruction with significantly larger search distances.
    - Fixed some precision issues in various Matrix methods

[danrbailey]

As mentioned, please remove templated interrupter from all of these API methods.

[danrbailey]

I would prefer if we don't add new methods with interrupter template arguments as it complicates explicit template instantiation. All the Houdini SOPs now use HoudiniInterrupter which sub-classes util::NullInterrupter, so fine to just provide util::NullInterrupter as an un-templated argument.

[danrbailey]

Do the setUnsafe() and getUnsafe() methods resolve the performance issues or is there something else you gain (simd?) from going directly to the buffers?