Adjust main history with every new root position
this patch dampens down main history to 3/4 of it value for all possible moves
at the start of ID loop, making it partially refresh with every new root
position.
Passed STC:
https://tests.stockfishchess.org/tests/view/694e33ff572093c1986d7234
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 115520 W: 30164 L: 29735 D: 55621
Ptnml(0-2): 395, 13192, 30192, 13551, 430
Passed LTC:
https://tests.stockfishchess.org/tests/view/6950cbe6572093c1986d816c
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 63672 W: 16480 L: 16114 D: 31078
Ptnml(0-2): 46, 6524, 18329, 6892, 45
closes https://github.com/official-stockfish/Stockfish/pull/6504
bench 2710946