Map cancelled request body uploads to OperationCanceledException in AndroidMessageHandler

[Copilot]

When a caller cancels the CancellationToken while AndroidMessageHandler is still uploading a request body (e.g. a PUT whose body the server delays reading), the cancellation surfaced as WebException/IOException ("Socket closed") instead of an OperationCanceledException subtype, diverging from SocketsHttpHandler.

The cancellation callback disconnects the socket, so the in-flight CopyToAsync to httpConnection.OutputStream throws Java.IO.IOException, which was then wrapped into a WebException by DoSendAsync. The response-body read path already mapped these to cancellation; the request-upload path did not.

Changes

• WriteRequestContentToOutput: catch transport exceptions thrown during the body copy when cancellation has been requested, and rethrow as System.OperationCanceledException tied to the caller's token.
• ShouldMapToCancellation: hoisted from the nested CancellationAwareResponseStream to the enclosing AndroidMessageHandler so the upload and response-read paths share one mapping rule (no change to the existing response-read behavior).
• Test: RequestBodyUploadCancellationIsPrompt stalls a raw-socket server after reading the request headers, streams a large body in chunks until the send buffer blocks, cancels mid-upload, and asserts a prompt OperationCanceledException.

try {
    await stream.CopyToAsync (httpConnection.OutputStream!, 4096, cancellationToken).ConfigureAwait (false);
} catch (Exception ex) when (ShouldMapToCancellation (ex, cancellationToken)) {
    throw new System.OperationCanceledException ("Request body upload was canceled.", ex, cancellationToken);
}