Do not build raw type descriptors for types with no type parameters.

Instead use the unparameterized version. The main issue is that for types with no type variables the interning keys are the same for the unparameterized and the raw type but their internals differ and can cause errors if an raw type is returned instead of the unparameterized type.

PiperOrigin-RevId: 589809769

transpiler/java/com/google/j2cl/transpiler/ast/TypeDeclaration.java

@@ -548,6 +548,15 @@ public int getMaxInterfaceDepth() {
    */
   @Memoized
   public DeclaredTypeDescriptor toRawTypeDescriptor() {
+    if (getTypeParameterDescriptors().isEmpty()) {
+      // The type does not declare any type variables, the raw type should equivalent to the
+      // unparameterized type. Return the nullable version explicitly since the unparameterized
+      // type descriptor is created with the default nullability of the scope.
+      return toUnparameterizedTypeDescriptor().toNullable();
+    }
+
+    // TODO(b/315520047): Evaluate whether this deep recursive construction of raw types is correct
+    // or if the raw types should always be equivalent to the unparameterized type.
     return DeclaredTypeDescriptor.newBuilder()
         .setTypeDeclaration(this)
         .setEnclosingTypeDescriptor(