Mix alpha and statScore for reduction

Mix alpha and statScore for reduction

Idea by @xoto10, and tuning by @FauziAkram.

Passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 57832 W: 15540 L: 15199 D: 27093
Ptnml(0-2): 207, 6343, 15477, 6680, 209
https://tests.stockfishchess.org/tests/view/6338db6f35f43d649ff60fdc

passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 50968 W: 13770 L: 13440 D: 23758
Ptnml(0-2): 25, 4905, 15306, 5211, 37
https://tests.stockfishchess.org/tests/view/6339777035f43d649ff62686

Links to the tuning sessions:
https://tests.stockfishchess.org/tests/view/63345725a004bed9a2e47b28
https://tests.stockfishchess.org/tests/view/63345728a004bed9a2e47b2a

closes https://github.com/official-stockfish/Stockfish/pull/4183

Bench: 4426602