Convert built-in blueprints to TypeScript

[cafreeman]

This PR is the ember.js counterpart to the work done in ember-cli to add support for typescript blueprints, both of which constitute the implementation of emberjs/rfcs#776.

This PR converts many (though not all) of the built-in ember blueprints. Notably, it excludes the mixin blueprint as well as the older test blueprints for both mocha and qunit. The only test blueprints that were converted were the post-testing overhaul blueprints (i.e. the ones that are now the defaults).

In order to prevent any compatibility issues that could arise from someone upgrading ember-source while still on an older version of Ember CLI, this PR also includes a polyfill for the typescript blueprint functionality.

[cafreeman]

Will update this to ^1.0.0 once we know there aren't any other changes needed.

[rwjblue]

Can we call this "owner" instead? In practice, that is what it is...

Suggested change

	export function initialize(appInstance) {
	export function initialize(owner) {

[rwjblue]

This looks great!!! I think the only thing left is to feature flag this so that we can easily toggle it on/off without reverting. Unfortunately, we don't have infrastructure setup to be able to read the @ember/canary-features module in node-land so it's a tad more annoying/difficult that more standard runtime feature flagging.

What I think we should do is:

• Create a shared utility at blueprints/-can-emit-typescript.js, that looks something like:

// TODO: this should be reading from the @ember/canary-features module
// need to refactor broccoli/features.js to be able to work more similarly
// to https://github.com/emberjs/data/pull/6231
const EMBER_TYPESCRIPT_BLUEPRINTS = false;

module.exports = function() {
  return 'EMBER_TYPESCRIPT_BLUEPRINTS' in process.env 
    ? process.env.EMBER_TYPESCRIPT_BLUEPRINTS
    : EMBER_TYPESCRIPT_BLUEPRINTS;
};

• Then update the polyfill to accept a second parameter (either options or a boolean) that allows us to force downlevel everyone to .js
• Then update the blueprints here to test with that environment variable on and off (I think the output is actually nearly identical, with the only difference being the extension?)

[rwjblue]

Chatted with @cafreeman offline, and I think he's come up with a better (and simpler) way to do the feature flagging.

[rwjblue]

Eeeck. Looks like we have some conflicts now, my apologies RE: the delays landing this.

@cafreeman - Mind rebasing / fixing things up?

[cafreeman]

@rwjblue Just resolved all the conflicts, we should be good to go now!