Merge pull request #506 from billsacks/fix_xgrid_reproducibility

Fix xgrid reproducibility by using srcTermProcessing=0 for all xgrid FieldRegridStore calls

### Description of changes

Use srcTermProcessing=0 for all xgrid FieldRegridStore calls.

This is needed for bit-for-bit reproducibility. Most of the calls to FieldRegridStore weren't setting srcTermProcessing at all; this can lead to irreproducibility of the results. Two of the calls had srcTermProcessing set to 1 before, which leads to reproducibility but (according to Gerhard Theurich) is often worse for performance than a value of 0.

Note that we use a value of 0 in the calls in med_map_mod.

### Specific notes

Contributors other than yourself, if any: Guidance from @oehmke and @theurich

CMEPS Issues Fixed (include github issue #): Resolves #505 

Are changes expected to change answers? YES: roundoff-level differences expected for runs with `aoflux_grid = "xgrid"` (but those runs had expected roundoff-level differences from run to run before this fix anyway)

Any User Interface Changes (namelist or namelist defaults changes)? No

### Testing performed
Please describe the tests along with the target model and machine(s) 
If possible, please also added hashes that were used in the testing

In the context of cesm3_0_alpha03c, with the change here put on top of the change in #501, ran `REP_Ld2.ne30pg3_t232.BLT1850.derecho_intel.allactive-xgrid`, where the `xgrid` testmod contained:

include_user_mods:
```
../defaultio
```

user_nl_cpl:
```
aoflux_grid = "xgrid"
```

mediator/med_phases_aofluxes_mod.F90

@@ -780,14 +780,16 @@ subroutine med_aofluxes_init_xgrid(gcomp, aoflux_in, aoflux_out, rc)
     type(ESMF_Mesh)      :: xch_mesh
     real(r8), pointer    :: dataptr(:)
     integer              :: fieldcount
-    integer              :: stp ! srcTermProcessing is declared inout and must have variable not constant
+    integer              :: srcTermProcessing_Value ! srcTermProcessing is declared inout and must have variable not constant
     type(ESMF_CoordSys_Flag)           :: coordSys
     real(ESMF_KIND_R8)    ,allocatable :: garea(:)
     character(len=*),parameter :: subname=' (med_aofluxes_init_xgrid) '
     !-----------------------------------------------------------------------
 
     rc = ESMF_SUCCESS
 
+    srcTermProcessing_Value = 0
+
     ! Get the internal state from the mediator Component.
     nullify(is_local%wrap)
     call ESMF_GridCompGetInternalState(gcomp, is_local, rc)
@@ -877,23 +879,26 @@ subroutine med_aofluxes_init_xgrid(gcomp, aoflux_in, aoflux_out, rc)
     dataptr(:) = 1.0_r8
 
     ! create agrid->xgrid route handles
-    call ESMF_FieldRegridStore(xgrid, field_a, field_x, routehandle=rh_agrid2xgrid, rc=rc)
+    call ESMF_FieldRegridStore(xgrid, field_a, field_x, routehandle=rh_agrid2xgrid, &
+         srcTermProcessing=srcTermProcessing_Value, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return
     call ESMF_FieldRegridStore(xgrid, field_a, field_x, routehandle=rh_agrid2xgrid_2ndord, &
-         regridmethod=ESMF_REGRIDMETHOD_CONSERVE_2ND, rc=rc)
+         regridmethod=ESMF_REGRIDMETHOD_CONSERVE_2ND, srcTermProcessing=srcTermProcessing_Value, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return
     if (trim(coupling_mode) == 'cesm') then
-       stp = 1
        call ESMF_FieldRegridStore(field_a, field_x, routehandle=rh_agrid2xgrid_bilinr, &
-            regridmethod=ESMF_REGRIDMETHOD_BILINEAR, dstMaskValues=(/0/), srcTermProcessing=stp, rc=rc)
+            regridmethod=ESMF_REGRIDMETHOD_BILINEAR, dstMaskValues=(/0/), &
+            srcTermProcessing=srcTermProcessing_Value, rc=rc)
        if (chkerr(rc,__LINE__,u_FILE_u)) return
        call ESMF_FieldRegridStore(field_a, field_x, routehandle=rh_agrid2xgrid_patch, &
-            regridmethod=ESMF_REGRIDMETHOD_PATCH, dstMaskValues=(/0/), srcTermProcessing=stp, rc=rc)
+            regridmethod=ESMF_REGRIDMETHOD_PATCH, dstMaskValues=(/0/), &
+            srcTermProcessing=srcTermProcessing_Value, rc=rc)
        if (chkerr(rc,__LINE__,u_FILE_u)) return
     end if
 
     ! create xgrid->zgrid route handle
-    call ESMF_FieldRegridStore(xgrid, field_x, field_a, routehandle=rh_xgrid2agrid, rc=rc)
+    call ESMF_FieldRegridStore(xgrid, field_x, field_a, routehandle=rh_xgrid2agrid, &
+         srcTermProcessing=srcTermProcessing_Value, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return
 
     ! destroy temporary field
@@ -911,12 +916,14 @@ subroutine med_aofluxes_init_xgrid(gcomp, aoflux_in, aoflux_out, rc)
     call ESMF_FieldGet(field_o, farrayptr=dataptr, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return
     dataptr(:) = 1.0_r8
-    call ESMF_FieldRegridStore(xgrid, field_o, field_x, routehandle=rh_ogrid2xgrid, rc=rc)
+    call ESMF_FieldRegridStore(xgrid, field_o, field_x, routehandle=rh_ogrid2xgrid, &
+         srcTermProcessing=srcTermProcessing_Value, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return
-    call ESMF_FieldRegridStore(xgrid, field_x, field_o, routehandle=rh_xgrid2ogrid, rc=rc)
+    call ESMF_FieldRegridStore(xgrid, field_x, field_o, routehandle=rh_xgrid2ogrid, &
+         srcTermProcessing=srcTermProcessing_Value, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return
     ! call ESMF_FieldRegridStore(xgrid, field_o, field_x, routehandle=rh_ogrid2xgrid_2ndord, &
-    !      regridmethod=ESMF_REGRIDMETHOD_CONSERVE_2ND, rc=rc)
+    !      regridmethod=ESMF_REGRIDMETHOD_CONSERVE_2ND, srcTermProcessing=srcTermProcessing_Value, rc=rc)
     ! if (chkerr(rc,__LINE__,u_FILE_u)) return
     call ESMF_FieldDestroy(field_o, rc=rc)
     if (chkerr(rc,__LINE__,u_FILE_u)) return