[ffigen] Support transitive categories of built-in types

[liamappelbe]

The core of the fix was simple: in FindDirectTransitiveDepsVisitation, I had to add a special case for the categories of interfaces defined in package:objective_c. But this caused a bunch of problems, so most of the PR is fixing the downstream effects of this change.

• In ListBindingsVisitation, I had to union all the directTransitives into the transitives to fix a bug where these new categories were missing all their SELs, msgSends, and class objects.
• In the visitors, I had to make a distinction between directlyIncluded (stuff that's explicitly mentioned in the config), and indirectlyIncluded (like super types, which we want to fully codegen even when they're not explicitly mentioned in the config). This fixes a bug where all of NSObject's categories were being generated even though the user didn't ask for them.
• Had to start tracking which categories were in package:objective_c (ObjCBuiltInFunctions.builtInCategories), so we don't codegen them in user bindings

Fixes #1820

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
objective_c	Breaking	4.1.0	5.0.0-wip	5.0.0	✔️

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

[coveralls]

coverage: 90.511% (+1.9%) from 88.604%
when pulling f776f75 on transcat
into ca5f3d2 on main.