Convert to V2 format

[ef4]

This converts to embroider v2 format, as one of our first examples of how to do that. The plan would be to land this and a few others and then extract the learned best-practices into an actual blueprint.

• merge and release the new utils in @embroider/addon-shim we depend on
• get embroider scenario passing -- there is a silly case embroider doesn't handle correctly in adjust-imports-plugin that is under-tested
• review top-level dotfiles for anything leftover that isn't needed
• document how to manage dependencies of test app
• document how to upgrade test app
• document scenarios.js and add to scripts as appropriate
  • how to run all
  • how to list
  • how to run one
  • how to output and debug one
• add default output from scenario-tester to gitignore
• nice-to-have: Support node_modules/.bin when linking deps stefanpenner/node-fixturify-project#56

[ef4]

This is a complete example now.

There are some further enhancements I have coming down the pipe to make the DX more familiar. The big one is adding a build step that takes care of template inlining so that the authored addon code can use normal template colocation, while the published code will be explicit.

[ef4]

Now this has its own small & fast build pipeline based on rollup. It takes care of template-colocation, and it generates your appTree for you, so you don't need to keep all those reexport-only files around.

[ef4]

I'm going to merge this to make it easier to iterate on. Happy to take feedback and get some consensus before cutting a release.