[NFC][OpenMP][MLIR] Add test for lowering parallel workshare GPU loop (#76144)

This test checks if MLIR code is lowered according to schema presented
below:

func1() {
    call __kmpc_parallel_51(..., func2, ...)
}

func2() {
   call __kmpc_for_static_loop_4u(..., func3, ...)
}

func3() {
   //loop body
}