DataCollection phase 2: propagate to native (Android/Cocoa)

Part of #5420. Phase 2 — consumer migration (.NET-specific).

Propagate `DataCollection` to the native layers:

- `src/Sentry/Platforms/Android/SentrySdk.cs:63` and `src/Sentry/Platforms/Cocoa/SentrySdk.cs:37` currently forward `options.SendDefaultPii` to the Java/Cocoa SDKs.
- Until sentry-java / sentry-cocoa implement the DataCollection spec: down-convert the resolved config to the native `sendDefaultPii` boolean **conservatively** (only `true` when the resolved config is at least as permissive as legacy-true).
- Forward `FrameContextLines` / `StackFrameVariables` to native equivalents where they exist (context lines are populated by the native layers, not managed code).
- Track native-SDK parity as follow-ups; revisit this mapping when sentry-java / sentry-cocoa ship their own `dataCollection`.

Start with src/Sentry/Platforms/Android/SentrySdk.cs:63 and src/Sentry/Platforms/Cocoa/SentrySdk.cs:37, then inspect how the resolved DataCollection configuration is currently forwarded. Verify conservative sendDefaultPii conversion and forwarding of FrameContextLines and StackFrameVariables where native equivalents exist. Done means both native integrations follow the stated mapping and native-SDK parity is recorded as a follow-up.

Written by the indexing model from the issue text.