Issue #2259 - Update Intl.* Object-ness to ECMA-402, 4th edition

- turn each Intl object into a NativeObject subclass
- create them as PlainObject
- ensure correct type is passed in self-hosted code
- implement legacy constructor semantics for DateTime&NumberFormat
- store internals on object slot instead of JS WeakMap

Based-on: m-c 1328386, 1332604

js/src/jit-test/tests/auto-regress/bug1263558.js

@@ -13,5 +13,5 @@ evalcx(`
     ');
     oomTest(() => eval('Array(..."")'));
     if ('Intl' in this)
-        Intl.NumberFormat.prototype.format(0);
+        new Intl.NumberFormat().format(0);
 `, newGlobal());

js/src/jit-test/tests/basic/bug920484.js

@@ -4,15 +4,8 @@ load(libdir + "asserts.js");
 // any value except "best fit" or "lookup" is okay.
 Object.prototype.localeMatcher = "invalid matcher option";
 
-// The Intl API may not be available in the testing environment. Note that |hasOwnProperty("Intl")|
-// initializes the Intl API if present, so this if-statement needs to appear after "localeMatcher"
-// was added to Object.prototype.
+// The Intl API may not be available in the testing environment.
 if (this.hasOwnProperty("Intl")) {
-    // Intl prototypes are properly initialized despite changed Object.prototype.
-    Intl.Collator.prototype.compare("a", "b");
-    Intl.NumberFormat.prototype.format(10);
-    Intl.DateTimeFormat.prototype.format(new Date);
-
     // Intl constructors no longer work properly, because "localeMatcher" defaults to the invalid
     // value from Object.prototype. Except for Intl.DateTimeFormat, cf. ECMA-402 ToDateTimeOptions.
     assertThrowsInstanceOf(() => new Intl.Collator(), RangeError);

js/src/jit-test/tests/ion/bug913749.js

@@ -15,6 +15,7 @@ for (var i = 0; i < 3; i++) {
 	x.toString();
 	assertEq(0, 1);
     } catch (e) {
-	assertEq(e.message, "y is undefined");
+	assertEq(e.message === "y is undefined" ||
+		 e.message === "undefined has no properties", true);
     }
 }