Pr/batched point cloud

[AlexMWells]

Description

Implement Batched pointcloud_search, pointcloud_get, and pointcloud_write.

Updated behavior of scalar pointcloud_search and pointcloud_get to not code gen branch with code gen runtime error for maxpoints/num_points larger than array size. Instead now it codgens a clamp of the maxpoints/num_points to the arraysize. This allows code to continue executing, and if accessed outside of the range, existing codgen range checks will still emit a runtime error.

Extracted class PointCloud definition and some helper functions to pointcloud.h so it can be shared between batched and scalar implementation.
Moved PointCloud out of anonymous namespace to OSL::pvt so a single implementation (including static maps) could be shared between batched and scalar implementation.

Refactored implementation of
template<typename DataT, int WidthT> struct Masked;
template struct Ref;

to flatten class hierarchy and fix bug where derivatives of unbounded arrays could not be constructed, IE:
MaskedDx<int[]> myDeriv(ptr, arraylength);

Added MaskedData::assign_val_lane_from_scalar
Renamed MaskedData::assign_val_from to MaskedData::assign_val_from_wide
Renamed MaskedData::assign_all_from to MaskedData::assign_all_from_scalar

Updated BatchedAnalysis to indicate that results of pointcloud_search, pointcloud_get, and pointcloud_write are always varying regardless of the symbols passed in.
Updated debugging in BatchedAnalysis to emit unmangled symbol names.

Properly implement (was broken previously) BatchedBackendLLVM::llvm_zero_derivs(const Symbol& sym, llvm::Value* count) including using code gen loop to reduce code bloat.

Fixed bug in llvm_gen for raytpye where the wrong type was passed as a name parameter . Only showed up when trying regression tests with optimizations disabled.

Tests

Expanded testsuite/pointcloud adding 2 additional write cloud tests and 10 additional read cloud including conditionally reading/writing and varying filename, maxpoints, and sort arguments.

Checklist:

• I have read the contribution guidelines.
• I have previously submitted a Contributor License Agreement.
• I have updated the documentation, if applicable.
• I have ensured that the change is tested somewhere in the testsuite (adding new test cases if necessary).
• My code follows the prevailing code style of this project.

[lgritz]

LGTM. I'm going to merge now so you can move on. There was one place I spotted an incorrect comment in testing.cmake, we can just fix that on the next PR.

[lgritz]

Oh neat, if a committer expresses a review comment as a "suggestion", it lets you merge the suggestions directly!