Extract Nbnxm::KernelOutputs from nbnxn_atomdata_t

This separates the Nbnxm kernel input data and responsibilities in nbnxn_atomdata_t from those related only to kernel output. This allows nbnxn_atomdata_t to be const during more parts of pair search.

No functionality changes.

Renamed "clear" to "zero" as appropriate to avoid ambiguity with std::vector::clear().

Eliminates the kernel_common.cpp file now that there is a class that can handle its functionality.

Some incidental typo fixes and minor modernization of SIMD function dispatch.

Refs #5020