Convert code to C++ 20

[robertapplin]

Convert code to use C++ 20 features:

• Use std::erase_if instead of std::remove_if and erase

To do

• Tidy up the calculation of the velocity (similar to how you did the acceleration)
• m_gravitational_constant feels like it should be a variable in caps at the top of the file
• Remove bodyNames if possible?
• Can be const:
  

  N-Body-Simulations/cpp/simulator/src/NBodySimulator.cpp

  Line 249 in 0190c94

  auto acceleration = calculateAcceleration(targetBody);

• Move simulation calculation code to a helper file
• Use shared_ptr for bodies instead of unique_ptr