std::trivially-copyable requirement for kernel parameters too strong

[eyalroz]

We currently require all (decayed types of) parameters to kernel functions satisfy the TriviallyCopyable C++ named set of requirements:

• Scalar types
• Trivially copyable classes, i.e. classes satisfying following requirements:
  • At least one copy constructor, move constructor, copy assignment operator, or move assignment operator is eligible
  • Every eligible copy constructor (if any) is trivial
  • Every eligible move constructor (if any) is trivial
  • Every eligible copy assignment operator (if any) is trivial
  • Every eligible move assignment operator (if any) is trivial
  • Has a trivial non-deleted destructor
• Arrays of TriviallyCopyable objects

That's too strong of a requirement. It's enough for us that the CUDA driver be able to copy the representation bytes of the class/struct, and construct a representation on the GPU using those bytes. The existence of other operators and ctors is inconsequential (well, I think so, any way). So, let's weaken the use std::is_trivially_copyable to std::is_trivially_copy_cosntructible.