Make setNValue allocate objects in temporary string pool, if needed 

Based on the test query, I was expecting VC2 and VB2 to be declared as 64 bytes or larger to force the CASE WHEN's result type to be potentially non-inlined. Sure, as our implementation CURRENTLY stands, it does not bother to be clever enough to determine that EVERY possible branch of the CASE WHEN is inlinable, so the result -- and any temp tuple storage that may follow could safely/optimally be inlined, but that's a conceivable future. In that future, this test would liklely continue to pass, but I think that in a larger sense it will fail -- to prove that ENG-6666 has not regressed. A mix of inlined and outlined sizes proves this point in a more implementation-independent way.