Rename "Coefficients" in lbm/refinement/

Meeting on 28.06.2023

Rename Coefficients to InterpolationCoefficients, since the current name is to vague.

The coefficients are used in various interpolations not just for refinement, e.g. interpolation between grids and the non-equilibrium initialization. So we want to move it to a separate folder named interpolation.

new folder structure:

• interpolation
  • InterpolationCoefficients
• refinement
  • InterpolationCF
  • InterpolationFC

Remark on calculateCoefficients(): "LaplaceRho" and "extrapolation for the refinement into the wall" (aka offsets) are specific to the grid refinement. The other calculations are more general and can be used for other interpolation as well. Therfore, we may want to refactor it in the future.