Quadratic smallnet threshold with re-evaluation

Quadratic smallnet threshold with re-evaluation

The threshold now decreases more quickly as pawn count decreases,
using the smallnet more compared to before.

Combo of two eval patches:
https://tests.stockfishchess.org/tests/view/66576c5f6b0e318cefa8d26e
https://tests.stockfishchess.org/tests/view/664ced40830eb9f886616a77

Passed STC:
https://tests.stockfishchess.org/tests/view/66588c136b0e318cefa8ff21
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 112608 W: 29336 L: 28908 D: 54364
Ptnml(0-2): 344, 13223, 28718, 13699, 320

Passed LTC:
https://tests.stockfishchess.org/tests/view/6658c8786b0e318cefa900f5
LLR: 2.96 (-2.94,2.94) <0.50,2.50>
Total: 108288 W: 27493 L: 27026 D: 53769
Ptnml(0-2): 54, 11821, 29930, 12282, 57

closes https://github.com/official-stockfish/Stockfish/pull/5323

bench 1728074