Negative extension for ttMove that is less than alpha and value
in the context of singular extensions
Passed STC:
https://tests.stockfishchess.org/tests/view/626047e8b03f22647441ade0
LLR: 2.97 (-2.94,2.94) <0.00,2.50>
Total: 50296 W: 13410 L: 13108 D: 23778
Ptnml(0-2): 196, 5548, 13370, 5826, 208
Passed LTC:
https://tests.stockfishchess.org/tests/view/6260a513b03f22647441b970
LLR: 2.96 (-2.94,2.94) <0.50,3.00>
Total: 83896 W: 22433 L: 22054 D: 39409
Ptnml(0-2): 49, 8273, 24938, 8626, 62
closes https://github.com/official-stockfish/Stockfish/pull/3995
bench: 7729968