Default more types to non-null

ocaml/testsuite/tests/typing-layouts-arrays/basics.ml

@@ -280,7 +280,7 @@ end
 Line 9, characters 24-35:
 9 |   let f2 idx : int32# = get arr idx
                             ^^^^^^^^^^^
-Error: This expression has type ('a : float64 mod non_null)
+Error: This expression has type ('a : float64)
        but an expression was expected of type int32#
        The layout of int32# is bits32, because
          it is the primitive bits32 type int32#.

ocaml/testsuite/tests/typing-layouts/layout_poly.ml

@@ -84,7 +84,7 @@ Line 4, characters 63-68:
 4 |   let () = Format.printf "%f %s\n" (F.to_float (id' #1.)) (id' "abc")
                                                                    ^^^^^
 Error: This expression has type string but an expression was expected of type
-         ('a : float64 mod non_null)
+         ('a : float64)
        The layout of string is value, because
          it is the primitive value type string.
        But the layout of string must be a sublayout of float64, because
@@ -543,7 +543,7 @@ external id : ('a : any) ('b : any). 'a -> 'b = "%identity" [@@layout_poly]
 Line 2, characters 28-32:
 2 | let f (x: float#): int64# = id x
                                 ^^^^
-Error: This expression has type ('a : float64 mod non_null)
+Error: This expression has type ('a : float64)
        but an expression was expected of type int64#
        The layout of int64# is bits64, because
          it is the primitive bits64 type int64#.

ocaml/typing/jkind.ml

@@ -560,7 +560,7 @@ module Const = struct
                   { layout = jkind.layout;
                     modes_upper_bounds = Modes.max;
                     externality_upper_bound = Externality.max;
-                    nullability_upper_bound = Nullability.max
+                    nullability_upper_bound = Nullability.Non_null
                   };
                 name = Layout.Const.to_string jkind.layout
               }