cloud_firestore should throw own exceptions

[kroikie]

As of cloud_firestore v0.8.0, all exceptions coming from the plugin are PlatformException. This makes it hard to catch specific problems.

For example, this is what I get from a regular transaction timeout exception:

PlatformException(9, Transaction failed all retries., null)
#0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:551:7)
#1      MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:279:18)
<asynchronous suspension>
#2      Firestore.runTransaction (file:///Users/filiph/dev/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.8.0/lib/src/firestore.dart:115:10)

In this particular example, I would love to have a TimeoutException instead, and catch only that.

cc @kroikie @bparrishMines

[kroikie]

@filiph

The issue at flutter/flutter#22440 has been closed and moved here. Future collaboration on this issue will be done here.

[Ehesp]

Duplicate #1223