Upgrade v2 tracking branch to Ember 3.13

[mansona]

This PR is to upgrade the v2 tracking branch's Ember version to 3.13 to allow for ember-learn/guidemaker-ember-template#78 to pass CI

As you can see, this PR does not target master. This is targeting a v2.x tracking branch that starts from the latest version of the v2.x series: v2.5.0.

This PR has been a tough one to get right because it's essentially full-on time travel coding 🙃 I had to upgrade and migrate a few things to be closer to what master does to even get this to work. If it passes tests I wouldn't worry too much because it will be tested properly downstream 👍

One problem with this change is that I had to drop Ember 3.4 and 3.8 from the test matrix because a dependency moved to co-location which needs a certain minimum version of Ember to work. This technically makes this a breaking change but we can't do that because v3 is already taken 🙈

We have a few options when it comes to dealing with this technical breaking change:

• do nothing because we're pretty sure we know all the apps using v2.x of the ember-styleguide have been upgraded past 3.8
• not release this to npm so that people with ^ dependencies won't have a broken experience because they won't get a broken upgrade automatically
• release it to npm as a pre-minor version, which has the benefit of working fine with npm but it would need an explicit opt-in from anyone using it as a dependency (i.e. will avoid the automatic upgrade problem)

Once we agree on how we want to proceed with the release we can get this merged and I can release it in the agreed manor 👍

[jenweber]

Thank you!

[mansona]

We discussed this in Discord and we have agreed to got with option 3 for the release of this one:

release it to npm as a pre-minor version, which has the benefit of working fine with npm but it would need an explicit opt-in from anyone using it as a dependency (i.e. will avoid the automatic upgrade problem)

I will release this after it is merged 👍