Extend rfl::AllowRawPtrs to std::string_view

[lixin-wei]

Support deserializing std::string_view as discussed in #454 (comment)

[gemini-code-assist]

Summary of Changes

Hello @lixin-wei, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces support for deserializing std::string_view types, a feature previously unsupported due to memory safety concerns. The change allows std::string_view deserialization only when the rfl::AllowRawPtrs processor is explicitly used, signaling that the user is aware of and prepared to manage the lifetime of the underlying string data. This provides greater flexibility for advanced use cases while maintaining safety for default configurations.

Highlights

• Enable std::string_view Deserialization: I've enabled the deserialization of std::string_view types within the reflect-cpp library. Previously, this was explicitly disallowed due to the inherent dangers of std::string_view not owning its underlying data.
• Conditional Behavior with rfl::AllowRawPtrs: The std::string_view deserialization is now permitted only when the rfl::AllowRawPtrs processor is active. If rfl::AllowRawPtrs is not used, the system will continue to prevent std::string_view deserialization with a static_assert and an error, guiding users to std::string or the AllowRawPtrs processor.
• Memory Management for std::string_view: When rfl::AllowRawPtrs is enabled, the deserialized string data is now dynamically allocated using new char[] and copied from an intermediate std::string. The resulting std::string_view points to this newly allocated memory. Users are responsible for managing the lifetime of this dynamically allocated memory.
• New Test Case: A new test case has been added in tests/json/test_pointer_fields.cpp to validate the correct serialization and deserialization of std::string_view when rfl::AllowRawPtrs is applied.

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[gemini-code-assist]

Code Review

The code changes introduce the ability to deserialize std::string_view. However, the current implementation introduces a critical memory leak due to missing memory management for the allocated string data. The review highlights this issue in both the parser logic and the test case.