[CFE] Encapsulate int operations in separate classes for VM and JS

This refactoring achieves the following:

- Collect the integer operation semantics into one place instead of
having it sprinkled all over the constant evaluator with many
"if (targetingJavaScript)" tests.

- Avoid emitting the internal JavaScriptIntConstant node, which is
serialized as normal DoubleConstant nodes, thus achieving parity
between direct consumers and consumers seeing output that has been
serialized.

- Implement the JavaScript semantics for unsigned right shift.

- Fix truncating divide with a result outside int64 range incorrectly
clamping the result for JS targets.

- Fix positive hex constants >= 2^63 through int.fromEnvironment
producing negative values in dart2js.

- Clarify in Kernel documentation how numeric constants are represented
on VM vs JS targets.

Change-Id: If30bb2c2c77c54eff120b611b059c2ec726c99a0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/116525
Reviewed-by: Mayank Patke <fishythefish@google.com>

pkg/dev_compiler/test/nullable_inference_test.dart

@@ -495,7 +495,19 @@ Future expectNotNull(String code, String expectedNotNull) async {
   var actualNotNull = collector.notNullExpressions
       // ConstantExpressions print the table offset - we want to compare
       // against the underlying constant value instead.
-      .map((e) => (e is ConstantExpression ? e.constant : e).toString())
+      .map((e) {
+        if (e is ConstantExpression) {
+          Constant c = e.constant;
+          if (c is DoubleConstant &&
+              c.value.isFinite &&
+              c.value.truncateToDouble() == c.value) {
+            // Print integer values as integers
+            return BigInt.from(c.value).toString();
+          }
+          return c.toString();
+        }
+        return e.toString();
+      })
       // Filter out our own NotNull annotations.  The library prefix changes
       // per test, so just filter on the suffix.
       .where((s) => !s.endsWith('::_NotNull {}'))