HPCC-12714 Support EMBEDDED DATASET syntax (currently ignored)

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
I checked and this is the only instance of this syntax within our regression suits (inc. private). Since we are not deprecating the syntax:
    dataset(itemRecord) items{embedded};
(assuming I haven't grossly misunderstood anything) changing this to test for the newly working syntax leaves the old now untested with in the suite. This defeats the point of regression testing. Ok, the original test wasn't doing this explicitly.

I think that we should start making test explicit, somewhat independent, and have their filename reflect their cause. The later point, I have raised before, prevents future commits cannibalising old tests without respect of their use/need.