docs: Update Android WebView guidance for connected traces

[antonis]

Outcome

Replace the current Android WebView guidance — which states the SDK "doesn't interact with the mobile application's web views" — with setup for the new trace-connection support.

Acceptance criteria

• Documents how to inject the native trace context into a WebView (meta tags at document-start via evaluateJavascript), the host allow-list option, the requirement that the in-WebView page run @sentry/browser, and the entry-pageload scope limitation.
• Wording coordinated with the Apple and React Native WebView doc updates for cross-platform consistency.

References

• Meta-tag continuation contract the page should point to: https://docs.sentry.io/platforms/javascript/tracing/distributed-tracing/
• Current Android WebView page to replace: https://docs.sentry.io/platforms/android/configuration/webview/
• Cross-platform parity: RN docs issue (docs: Update React Native WebView guidance for connected traces sentry-react-native#6782), Apple docs issue

[linear-code]

JAVA-745