[jnigen] Support build.gradle.kts

[HosseinYousefi]

Closes #1904.

Added equivalent Kotlin stubs for build.gradle.kts to the groovy stubs when no build.gradle is found in the project. We don't have the infra to test this yet, tested it locally. Tracking issue for tests: #1155.

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
jni	None	0.14.1	0.14.1	0.14.1	✔️

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

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.

Package	Leaked API symbols
jni	_ReferenceType _opaque_pthread_mutex_t _opaque_pthread_cond_t _Dart_FinalizableHandle

This check can be disabled by tagging the PR with skip-leaking-check.

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.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

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

[coveralls]

coverage: 84.828% (-0.004%) from 84.832%
when pulling 30325c0 on gradle-kts
into 4928765 on main.