Split grid generation and remapping from step thermo

Move grid generation, remapping, and subsequent processes into a new
routine ALE_gridgen_and_remapping which is called immediately after
step_MOM_thermo.

Clean up inputs and local variables in step_MOM_thermo by removing
those only used for gid generation and remapping.

Routines that need to be done after step_thermo, grid generation
and remapping, regardless of use_ALE or not into another routine
since they do not make sense in ALE_gridgen_and_remapping.

Answers and diagnostics have not changed in Baltic case in ALE mode.
Testing still needs to be done layer mode and with particles.