Support transpile async await for ES2017 target

[JiaLiPassion]

🚀 Feature request

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Description

A clear and concise description of the problem or missing capability...

Now Angular can work properly for target ES2015, but if we want to build for target ES2017, the native async/await will not work because Zone.js can't monkey patch native async/await. (angular/angular#31730) But we still want the other ES2017+ native features.

Describe the solution you'd like

If you have a solution in mind, please describe it.

So if we can use some plugin of webpack with https://github.com/angular/angular-cli/tree/master/packages/angular_devkit/build_webpack, to process the bundle and only transpile the async/await code to generator, but keep all other ES2017+ code as native, it maybe a acceptable solution for now until we can find some other solutios.

Describe alternatives you've considered

Have you consid ered any alternative solutions or workarounds?

[clydin]

There have been some initial experiments into this type of mechanism. They mainly revolve around using babel for JavaScript transformation and TypeScript only for TypeScript conversion.
There is currently an issue tracking improved (more intelligent) transpilation here: #16170
Since there is already active discussion in that existing issue and it could also provide a solution to the zone.js async/await issue, I'm going to close this one.

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