[firebase_auth_web] Exceptions returned are incompatible with mobile

[buntagonalprism]

Issue Summary.
Any exception thrown by firebase_auth_web is a FirebaseError from package:firebase. On mobile a PlatformError is thrown instead. This makes it difficult to have cross-platform error handling logic.

For example, the following logic works great on mobile for handling users attempting to sign in with an unrecognised email address. But to handle errors from web with similar type-safety requires importing the web-only package:firebase to get the FirebaseError class, making it no longer mobile-compatible:

try {
  final user = await auth.signInWithEmailAndPassword(email: email, password: password);
  goToUserHome(user);
} on PlatformException catch (error, trace) {
  if (error.code == "ERROR_USER_NOT_FOUND") {
    showNotFoundWarning();
  } else {
    rethrow;
  }
} 

(The error codes are also different between mobile and web for the same causes, but that's from the underlying Firebase library not FlutterFire).

Desired Solution
firebase_auth_web should map any FirebaseError into a PlatformError to provide API compatability and cross-platform support with the mobile implementation. Or perhaps FirebaseError could be exposed as part of package:firebase_core or similar to avoid the need for a dependency on the web-only package:firebase.

[Ehesp]

Related: #1456

Different platform so leaving open.

[Ehesp]

This has been fixed in the latest release.