feat: Extend instanceof Support for GaxiosError

[danielbankhead]

Improve instanceOf Support for GaxiosError

There are a number of reasons instanceof could provide false-negatives:

• instanceof is broken when class extends Error type microsoft/TypeScript#13965 (comment)
• https://stackoverflow.com/questions/46618852/require-and-instanceof

This PR aims to keep instanceof consistent and predictable across builds, in a supported, conventional way:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/hasInstance
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/@@hasInstance#reverting_to_default_instanceof_behavior

Background for why this is needed:

• fix: Support 404 When GaxiosError != GaxiosError google-auth-library-nodejs#1707
• Unsuccessful response status code. Request failed with status code 404 google-auth-library-nodejs#1706

Future Follow-ups

In the future we could create a utility to support the functionality for any class. E.g.:

function addInstanceOfSupport<T extends Function>(
  constructor: T,
  pkgInfo: typeof pkg
) {
  // Generate unique, predictable symbol
  const symbol = Symbol.for(`${pkgInfo.name}-${constructor.name}`);
  // Set symbol on constructor
  const c = constructor as unknown as {[symbol]: string};
  c[symbol] = pkgInfo.version;

  // keep original call
  const original = constructor[Symbol.hasInstance];

  function instanceofWithSymbolCheck(instance: unknown) {
    if (
      instance &&
      typeof instance === 'object' &&
      symbol in instance &&
      instance[symbol] === pkgInfo.version
    ) {
      return true;
    }

    // fallback to original call
    return original.call(constructor, instance);
  }

  constructor[Symbol.hasInstance] = instanceofWithSymbolCheck;
}

// example
addInstanceOfSupport(GaxiosError, pkg);

🦕