[FEA] Add kernel launch wrapper

[PointKernel]

Is your feature request related to a problem? Please describe.
Currently, we are adding early exits in all bulk functions to avoid launching kernels with 0 threads. This is laborious and should be done in a more systematic way.

Describe the solution you'd like
As mentioned in #151 (review), a kernel launch wrapper is desired to automate skipping kernel launches for 0 threads.

[sleeepyjack]

That would be a simple if(std::distance(input_begin, input_end) == 0) return;?

[PointKernel]

That would be a simple if(std::distance(input_begin, input_end) == 0) return;?

@sleeepyjack Yeah, an early exit like that in a variadic template.