message: Add count_if as a macro function
  Alias for `sum(if(x, 1, 0))` where x is a boolean
diff: @@ -93,6 +93,7 @@ static DefaultMacro internal_macros[] = {
  {DEFAULT_SCHEMA, "generate_subscripts", {"arr", "dim", nullptr}, "unnest(generate_series(1, array_length(arr, dim)))"},
  {DEFAULT_SCHEMA, "fdiv", {"x", "y", nullptr}, "floor(x/y)"},
  {DEFAULT_SCHEMA, "fmod", {"x", "y", nullptr}, "(x-y*floor(x/y))"},
  + {DEFAULT_SCHEMA, "count_if", {"l", nullptr}, "sum(if(l, 1, 0))"},
  // algebraic list aggregates
  {DEFAULT_SCHEMA, "list_avg", {"l", nullptr}, "list_aggr(l, 'avg')"},
  