Add Gradle wrapper files for version 9.0-milestone-1

[Crucialjun]

• Added gradle-wrapper.properties to specify the distribution URL and settings.
• Included gradlew shell script for Unix-based systems to facilitate Gradle execution.
• Added gradlew.bat script for Windows to enable Gradle commands in a Windows environment.

[Copilot]

Pull Request Overview

This PR updates the project to use Gradle 9.0-milestone-1 and modernizes the build configuration by adding Gradle wrapper files and updating dependencies.

• Added Gradle wrapper files for version 9.0-milestone-1 to enable consistent build environments
• Updated flutter_lints dependency from ^3.0.1 to ^6.0.0 across multiple pubspec.yaml files
• Modernized Android build configuration with newer plugin syntax and updated dependencies

Reviewed Changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
libphonenumber_plugin/pubspec.yaml	Updated flutter_lints dependency to ^6.0.0
libphonenumber_plugin/example/pubspec.yaml	Updated flutter_lints dependency to ^6.0.0
libphonenumber_plugin/android/settings.gradle	Added plugin management configuration and updated plugin versions
libphonenumber_plugin/android/gradlew.bat	Added Gradle wrapper batch script for Windows
libphonenumber_plugin/android/gradlew	Added Gradle wrapper shell script for Unix systems
libphonenumber_plugin/android/gradle/wrapper/gradle-wrapper.properties	Added Gradle wrapper properties file specifying version 9.0-milestone-1
libphonenumber_plugin/android/build.gradle	Modernized build script with new plugin syntax and updated dependencies

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