Modify Provider to keep the latest flags even when it is remounted

[bufferings]

Requirements

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

Related issues

https://github.com/launchdarkly/react-client-sdk/issues/237

Describe the solution you've provided

Provide a clear and concise description of what you expect to happen.

Describe alternatives you've considered

Provide a clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context about the pull request here.