Style: Use qualified auto in C++ code

[arcondello]

We obviously use pointers types a lot in the C++ code. For example we do

auto x_ptr = graph.emplace_node<BinaryNode>();

IMO we should be using qualified auto in these places

auto* x_ptr = graph.emplace_node<BinaryNode>();

for readability.

Obviously there is a semantic difference if later we need to do say decltype(auto) but in most places we never inspect the auto and the latter conveys more meaning.

See

• LLVM Coding Standards: "Use auto & for values and auto * for pointers unless you need to make a copy."
• clang-tidy's readability-qualified-auto