MLNodeLaplacian: route mknewu through anisotropic sigma path

[drummerdoc]

Summary

When setMapped(true) is used, MLNodeLaplacian stores sigma with AMREX_SPACEDIM components so each velocity/flux direction can carry its own diffusivity. However, MLNodeLaplacian::updateVelocity and MLNodeLaplacian::getFluxes both read only m_sigma[amrlev][0][0] (sigma_x) and applied it to every velocity component, leaving the caller with

u_i = u_entry - sigma_x * (grad phi)_i

instead of the correct per-component

u_i = u_entry - sigma_i * (grad phi)_i

Add mlndlap_mknewu_ha (2D and 3D) as an anisotropic-sigma sibling of mlndlap_mknewu, and route both updateVelocity and getFluxes through it when m_use_mapped is true. 2D preserves the RZ axial correction. EB is intentionally left on the scalar sigma_x path: producing mlndlap_mknewu_eb_ha is a separate task and no in-tree consumer needs it today.

Downstream codes can detect the fix via the new feature macro AMREX_MLNODELAP_HAS_MKNEWU_HA in AMReX_MLNodeLaplacian.H.

Additional background

This was recognized and fixed as part of an effort to add mapped grids into PeleLMeX - PR coming soon.

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• include documentation in the code and/or rst files, if appropriate