For example, instead of

   if (dict.found("value"))
   {
       fvScalarField::operator=
       (
           Field<scalar>("value", dict, p.size())
       );
   }

can use more precise specifications, and also eliminate searching
the dictionary multiple times:

   const auto* eptr = dict.findEntry("value", keyType::LITERAL);

   //or:  dict.findCompat("value", {{"oldName" ... }}, keyType::LITERAL);

   if (eptr)
   {
       fvScalarField::assign(*eptr, p.size());
   }

STYLE: combine declaration of FieldBase into Field.H