Feature: #81601 - Add possibility to write tests in typeScript

See Issue #81601

Description

The core is using TypeScript as language already - now writing unit tests in TypeScript is also possible. The tsconfig.json now contains both JavaScript and TypeScript module path mappings, the Grunt file will take care of adjusting the paths for TypeScript as well.

Impact

Tests can now be written directly in TypeScript, making it easier to test TypeScript components, having auto-completion and IDE support. Tests written in TypeScript will be converted to JavaScript via the grunt task scripts and executed via the existing Karma configuration.