Add first test version of high level task stealing.

This means that high level tasks can be stolen and lays the groundwork for implementing different tasks like classic work stealing.
3 jobs from basic_taskmodel in 2 minutes 9 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #2695
build_cmake

00:36

 
  Test
passed #2696
run_tests

00:33

 
  Sanitizer
passed #2697
run_thread_sanitizer

00:58