Introduce pre-qsearch ttmove extensions at pv nodes
The idea is that we are about to dive into qsearch (next search depth is <= 0)
but since we have the move in transposition table we should extend that move
and evaluate it with more precise search - because branch seems important.
Passed STC:
https://tests.stockfishchess.org/tests/view/6699d2564ff211be9d4ec488
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 83104 W: 21789 L: 21401 D: 39914
Ptnml(0-2): 293, 9748, 21128, 10044, 339
Passed LTC:
https://tests.stockfishchess.org/tests/view/669b3f1a4ff211be9d4ec602
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 136098 W: 34636 L: 34111 D: 67351
Ptnml(0-2): 105, 14882, 37550, 15407, 105
closes https://github.com/official-stockfish/Stockfish/pull/5512
bench 1526129