fix: updating deprecated AndroidClientHandler to AndroidMessageHandler

[tanderson-ld]

Requirements

• [x] I have added test coverage for new or changed functionality
• [x] I have followed the repository's pull request submission guidelines
• [x] I have validated my changes against all supported platform versions Validated on Android

Related issues

https://github.com/launchdarkly/dotnet-client-sdk/issues/64#issuecomment-1866554447

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #222947: Dotnet MAUI support.