Improve memory handling of VtArrays

[cpichard]

Describe the feature you'd like When we extract a VtArray from a VtValue we sometime use a copy instead of a const reference, as the copy on write of VtArray shouldn't duplicate the buffer. However, when we call functions or operators on the extracted array, a copy of the whole buffer might be happening as the function called is not the const one. It can lead to unnecessary increase of memory. We want to chase down where it happens in the code and fix those redundant copies.

[autodesk-oss-arnold-bot[bot]]

Issue synced internally to ARNOLD-14852