[jnigen] Fix generic subinterfaces not specifying full type params

[HosseinYousefi]

Closes #2250. Classes that inherited a generic without specifying all type parameters were not generated. Filling the ones not specified with JObject?.

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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Files
pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[coveralls]

coverage: 78.958% (+1.2%) from 77.787%
when pulling 3d75bd2 on fix-method-move
into 6e675b3 on main.