Fix tangents in Osd::EvalLimitController

- don't rotate (s,t) coordinates but rotate the patch instead !

- refactor osd/cpuEvalLimitKernels to share Far::PatchTables cubic spline
  interpolation functions : this replaces tensor product formulation with
  weight matrices, which does not really impact performance here, but would
  have to be replaced when implementing regular gridding functions.

- fix OsdCpuEvalLimitController to not rotate coordinates and pass the rotation bitfields

- expose Far::PatchTables spline interpolation API (protected -> public)

- fix glEvalLimit tangent buffers (remove empty padding - see below)

- change policy for tangent buffers : the output buffer descriptor is
  **NO LONGER APPLIED** to tangent output buffers. Tangent primvar data
  buffers are no longer applying the offset and stride from the descriptor
  (because it doesn't make sense to share it). If more flexiblity is
  required, we will consider adding independent descriptors for the tangent
  buffers. This change will impact existing code that generates tangents
  with the EvalLimit controller.

fixes #370