Add support for WebViews

Enable connected traces across Android native code and WebViews by injecting the native trace ID for the JavaScript SDK to pick up.

* Evaluate trace propagation and span-linking approaches.
* Validate compatibility with the existing Android WebView configuration.
* Document constraints and recommend an implementation approach.

Reference: [Android WebView documentation]()

Start with the referenced Android WebView documentation and the repository's existing Android WebView configuration. Evaluate trace propagation and span-linking approaches, then validate compatibility with that configuration. Done means documenting constraints and recommending an implementation approach for injecting the native trace ID for the JavaScript SDK.

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