Utilize constituent object const_index routine

[peverwhee]

Once we have exposed the full constituent (ccpp_model_constituents_t) object via metadata (NCAR/ccpp-framework#597), we should update the following schemes to use the const_index method to grab a constituent index by its standard name (instead of what we're doing now, which is looping over all the constituents to get the index):

• sima_diagnostics/sima_state_diagnostics.F90
  • remove const_std_names and const_diag_names
  • grab the index using the newly exposed interface
  • if the constituent is present, call history_out_field/history_add_field
• any scheme that uses ccpp_const_get_idx
  • possible candidates: check_energy_chng, zm_diagnostics

const_index routine in the constituents object (in the CCPP framework):

subroutine ccp_model_const_index(this, index, standard_name, errcode, errmsg)
      ! Return index of metadata matching <standard_name>.
      ! <this> must be locked to execute this function

      ! Dummy arguments
      class(ccpp_model_constituents_t), intent(in)  :: this
      character(len=*),                 intent(in)  :: standard_name
      integer,                          intent(out) :: index
      integer,          optional,       intent(out) :: errcode
      character(len=*), optional,       intent(out) :: errmsg
      ! Local variables
      type(ccpp_constituent_properties_t), pointer  :: cprop => NULL()
      character(len=*), parameter :: subname = "ccp_model_const_index"

      if (this%const_props_locked(errcode=errcode, errmsg=errmsg, warn_func=subname)) then
         cprop => this%find_const(standard_name)
         if (associated(cprop)) then
            index = cprop%const_index()
         else
            index = int_unassigned
         end if
      else
         index = int_unassigned
      end if

   end subroutine ccp_model_const_index