Since ECMAScript brings some nice features in later releases (e.g.
native support for async / await), we upgrade our build chain to use
ES2017.

This removes a lot of polyfills introduced by TypeScript and it's
considered safe to upgrade the used ES standard as all browsers
supported by TYPO3 support this standard as well.

Resolves: #90199
Releases: master
Change-Id: I6d8257a368a3eb51e2fff4f7610c7826f209c7e7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63026


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>