Merge pull request #4450 from RosettaCommons/roccomoretti/clang_tidy_4
Clang tidy: modernize-use-nullptr
Another in the series of adding additional clang-tidy tests. This one is pretty much purely mechanical.
The big change was to fixedarray1/fixedarray0. These were changed to default initialize instead of zero initialize. This had the knock-on effect of requiring me to convert their internal store from a C-style array to a std::array, as well as changing a few places where there were fixedsizearrays of xyzVectors (which behave differently for zero vs. default initialization.)