[dart2wasm] Fix some errors in FutureOr normalization

This fixes two issues for the cases where `FutureOr` normalizes to
`Future`:

- Normalize to `Future` instead of `_Future`.
- Normalize `FutureOr<Never>?` to `Future<Never>?` instead of
  `Future<Never>`.

Change-Id: I3bcf96c71a7424cecd3872255660fa1513abdfc3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/271882
Reviewed-by: Joshua Litt <[email protected]>
Commit-Queue: Aske Simon Christensen <[email protected]>

Author: askeksa

sdk/lib/_internal/wasm/lib/class_id.dart

@@ -28,8 +28,8 @@ class ClassID {
   external static int get cidInt8ArrayView;
   @pragma("wasm:class-id", "dart.core#Object")
   external static int get cidObject;
-  @pragma("wasm:class-id", "dart.async#_Future")
-  external static int get cid_Future;
+  @pragma("wasm:class-id", "dart.async#Future")
+  external static int get cidFuture;
   @pragma("wasm:class-id", "dart.core#Function")
   external static int get cidFunction;
   @pragma("wasm:class-id", "dart.core#_Function")

sdk/lib/_internal/wasm/lib/type.dart

@@ -184,7 +184,7 @@ class _FutureOrType extends _Type {
   const _FutureOrType(super.isDeclaredNullable, this.typeArgument);
 
   _InterfaceType get asFuture =>
-      _InterfaceType(ClassID.cid_Future, isDeclaredNullable, [typeArgument]);
+      _InterfaceType(ClassID.cidFuture, isDeclaredNullable, [typeArgument]);
 
   // Removing a `?` from a type should not require additional normalization.
   @override
@@ -554,9 +554,10 @@ class _TypeUniverse {
     if (isTopType(typeArgument) || isObjectType(typeArgument)) {
       return typeArgument;
     } else if (typeArgument.isNever) {
-      return _InterfaceType(ClassID.cid_Future, false, [const _NeverType()]);
+      return _InterfaceType(
+          ClassID.cidFuture, isDeclaredNullable, [const _NeverType()]);
     } else if (typeArgument.isNull) {
-      return _InterfaceType(ClassID.cid_Future, true, [const _NullType()]);
+      return _InterfaceType(ClassID.cidFuture, true, [const _NullType()]);
     }
 
     bool declaredNullability =