Fixes #954.

1. Removed support for Node 8 and 10 unstructured logging since we no longer support those versions of Node.
2. Wrap all logging.error messages in an Error if none of the args are an error.

(2) makes sure that we get a stack trace in the log message, which is required for the Cloud Run data plane to send the log line to Cloud Error Reporting, where it shows up in the Firebase "Health" tab.

Tested with the following sample:

import { onRequest } from 'firebase-functions/v2/https';
import * as logger from 'firebase-functions/logger';

export const func = onRequest((req, res) => {
    logger.info("This is an info log");
    logger.error("This is an error log");
    logger.info("This is an info log with an error suffix", new Error("suffix"));
    logger.error("This is an error log with an error suffix", new Error("suffix"));
    res.send("OK");
    throw new Error("This is an unhandled error");
});

Cloud error reporting recorded all logger.error lines and the unhandled exception. The case with an Error suffix did not nest errors, which would cause the stack trace to be repeated.