[swift2objc] Generate initializers as public

[liamappelbe]

Generate initializers as public, except for the internal wrapperInitializer.

Fixes #2666

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:code_assets	0.19.7	already published at pub.dev
package:data_assets	0.19.3	already published at pub.dev
package:ffi	2.1.5-wip	WIP (no publish necessary)
package:hooks	0.20.1	already published at pub.dev
package:hooks_runner	0.23.0	already published at pub.dev
package:native_doc_dartifier	0.0.1-pre	already published at pub.dev
package:native_toolchain_c	0.17.2	ready to publish	native_toolchain_c-v0.17.2
package:swift2objc	0.1.0	already published at pub.dev
package:swiftgen	0.1.1	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions]

PR Health

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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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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no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/objective_c/lib/src/ns_input_stream.dart

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[coveralls]

coverage: 81.639% (+0.8%) from 80.791%
when pulling f662b0e on swft2objc_init
into 3ec5735 on main.