[TASK] Build JavaScript files using ECMAScript 6

Since TYPO3 v10 dropped support for Internet Explorer, JavaScript files
may be shipped using the ECMAScript 6 standard. External assets simply
get transpiled as far as possible. TypeScript loads the internal for ES6
and ES7 to generate native ECMAScript 6 builds.

Resolves: #89047
Releases: master
Change-Id: I5ab877ae07bba26e3953441040a519c628501b6b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61582


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>