[ffigen] Fix #1268

[liamappelbe]

There's a rareish bug where a specific interface type can be codegenned as a generic ObjCObjectBase. It can happen in methods or properties, in arguments or returns.

I'm not 100% sure what causes it, but it seems to happen when the interface has type params, and is forward declared. Eg, I was able to repro it in the test by writing a method that returns an NSArray<NSString*>*, and forward declaring NSArray and NSString instead of #importing their headers.

The bug is that in the AST these types show up as a CXType_ObjCObject instead of a CXType_ObjCInterface. Their structure is exactly the same as any other interface, but the different kind enum value means that they fall through our parsing switch and default to the generic object type. So the fix is just to add this enum value to the switch.

Fixes #1268

[github-actions]

PR Health

Breaking changes ⚠️

Package	Change	Current Version	New Version	Needed Version	Looking good?
objective_c	Breaking	7.1.0	7.2.0-wip	8.0.0 Got "7.2.0-wip" expected >= "8.0.0" (breaking changes)	⚠️

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API leaks ⚠️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

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objective_c	_Version

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License Headers ✔️

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

[coveralls]

coverage: 86.357% (+0.07%) from 86.29%
when pulling 82ff296 on bug1268
into deda4d1 on main.