Use getDOM util to get dom reference in glimmer2

[bantic]

When using ember canary (2.9.x), the this.renderer._dom property no
longer exists. This adds a util function to get access to the dom
property in a way that works in both contexts.

This makes it so ember-wormhole works correctly in ember canary 2.9.x when rendered in the browser, but there are some issues with ember-cli-fastboot
and ember canary (ember-fastboot/ember-cli-fastboot#258 and ember-fastboot/ember-cli-fastboot#255) that are not related to ember-wormhole. The code in this PR will work with ember canary and fastboot after those issues are resolved.

Fixes #64

[lukemelia]

Awesome, thanks for this @bantic. 👍

[cibernox]

Thank you sir!

[lukemelia]

@cibernox done https://github.com/yapplabs/ember-wormhole/releases/tag/0.4.1

[krisselden]

Are we just console hacking? I'm pretty certain the document used is available in both with the same container key

[cibernox]

@krisselden when I opened the issue ~2w ago I can assure that this.renderer._dom; wasn't there.

[bantic]

@krisselden @cibernox Yes, I can confirm — this.render._dom wasn't around in glimmer2 components when I worked on this.

[krisselden]

@bantic that is not what I meant

you are wanting document.createTextNode

document has been available as service:-document since before glimmer 2, this is still not public, but at least it is more stable and less indirect through many private APIs.