Add weighted d[uv]_dt_str diagnostics

This adds four new diagnostics building on the wind stress acceleration diagnostics du_dt_str, dv_dt_str

their thickness-weighted versions: h_du_dt_str, h_dv_dt_str (completing the set of diags from #7)
their viscous remnant fraction: du_dt_str_visc_rem, dv_dt_str_visc_rem (completing the set of diags from #10)

I did some quick tests with our NeverWorld2 setup, which confirm that online and offline multiplication by h and visc_rem_[uv], respectively, coincide (up to interpolation error and numerical noise, respectively). See the two figures below.

Thickness-weighted

test_h_du_dt_str

Viscous remnant fraction

test_du_dt_str_visc_rem

ocean-eddy-cpt / MOM6

Add weighted d[uv]_dt_str diagnostics #17

Thickness-weighted

Viscous remnant fraction