TypeScript:
Due to issues with upcoming TypeScript versions, the TypeScript sources
are moved into the Build directory before building JavaScript.

The unused Grunt task `tsdev` has been removed.

Additionally, some type defintions have been installed:

  yarn add --dev \
      @types/bootstrap-slider \
      @types/datatables.net \
      @types/chosen-js

Sass:
The Sass sources have been moved into the common "Sources" directory.
Those source files are moved to have a less cluttered Build directory.

Note: With this patch, all TypeScript files must be placed into
`Build/Sources/TypeScript` to be compiled by tsc again.

Resolves: #88043
Releases: master
Change-Id: I4d3e5f69564c38a35bf083652ea7262f5b85e4f3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60335


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Anja Leichsenring <aleichsenri...