ENH: Improve the handling of wall-function coefficients and blenders

Summary

• Fixes #1457 and #1966 (closed)
• Improves the handling of wall-function coefficients and blenders
• Standardises the output of wall-function entries
• Removes redundant and inconsistent virtual specifiers
• Modernises the code style
• Improves header file documentation
• Removes the blending option BINOMIAL2 from omegaWallFunction

Resolved bugs

Closes #1457, #1966 (closed)

Risks

• Silently replaces the default blending option BINOMIAL2 of the omegaWallFunction with the option BINOMIAL with n=2. In theory, both expressions are the same. Yet numerically, both expressions will yield negligible differences in floating-point decimals.

Tests

• Compilation (incl. submodules):
  • linux64ClangDPInt32Opt (clang11)
  • linux64GccDPInt32Opt
  • linux64GccSPDPInt64Debug
• Alltest: No change in output with respect to the develop HEAD + no error
• Verification: No change in output rhoSimpleFoam/simpleFoam/buoyantBoussinesqSimpleFoam