This patch updates some tools used for our assets generation toolchain.

Most notable changes:

- Since typescript-eslint has been updated to a new major version, its
  configuration changes slightly
- TypeScript is updated to 3.9

Executed commands:

  yarn add --dev \
      "@typescript-eslint/eslint-plugin"@^3.8.0 \
      "@typescript-eslint/parser"@^3.8.0 \
      "@typescript-eslint/typescript-estree"@^3.8.0 \
      autoprefixer@^9.8.6 \
      eslint@^7.6.0 \
      grunt-eslint@^23.0.0 \
      grunt-lintspaces@^0.9.0 \
      jasmine-core@^3.6.0 \
      karma@^5.1.1 \
      karma-coverage@^2.0.3 \
      karma-jasmine@^3.3.1 \
      terser@^5.0.0 \
      typescript@~3.9.0
  grunt build

Resolves: #91952
Releases: master, 10.4
Change-Id: Ib6726998bea0faf68e71d8374ee0d729a34b0c1e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65223


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Christian Kuhn <lolli@...>