Fix for Issue #2640: Resolve mu angular distributions of surface current

[zoeprieto]

Description

This PL addresses and resolves issue #2640 in the OpenMC repository, which pertains to the possibility of calculating the mu angular distribution of any surface current. I have added a MuSurface filter to be able to calculate such a distribution when used with a SurfaceFilter. Currently, the MuFilter only calculates the mu distribution for scattering angles and cannot be combined with a surface filter. On the other hand, the PolarFilter only calculates the polar angle distribution for a plane with the z-normal. Therefore, this allows us to calculate the mu distribution for a current on any of the OpenMC surfaces.

Fixes #2640

Checklist

• [x] I have performed a self-review of my own code
• [x] I have run clang-format (version 15) on any C++ source files (if applicable)
• [x] I have followed the style guidelines for Python source files (if applicable)
• [x] I have made corresponding changes to the documentation (if applicable)
• [x] I have added tests that prove my fix is effective or that my feature works (if applicable)