Simplify & improve stalemate detection
Change is functional because now we verify for stalemate also on captures and when not giving check.
Green STC test on stalemate-book
https://tests.stockfishchess.org/tests/view/682d878f6ec7634154f9ad2f
Elo: 2.29 ± 1.3 (95%) LOS: 100.0%
Total: 10000 W: 4637 L: 4571 D: 792
Ptnml(0-2): 2, 132, 4664, 202, 0
nElo: 12.42 ± 6.8 (95%) PairsRatio: 1.51
Green LTC test on stalemate-book
https://tests.stockfishchess.org/tests/view/682daa2d6ec7634154f9ad67
Elo: 0.80 ± 0.8 (95%) LOS: 96.9%
Total: 10000 W: 4727 L: 4704 D: 569
Ptnml(0-2): 0, 64, 4849, 87, 0
nElo: 6.51 ± 6.8 (95%) PairsRatio: 1.36
Passed non-regression test @ LTC
https://tests.stockfishchess.org/tests/view/682dd10d6ec7634154f9adb3
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 148512 W: 38135 L: 38046 D: 72331
Ptnml(0-2): 55, 15759, 42558, 15810, 74
N.B.: The unique concern I have, is that due changes in future a negative SEE
capture see might be returned in GOOD_CAPTURE stage. In this case the assert in
can_move_king_or_pawn() will trigger since we must guarantee that all moves
(also quiets) are generated in movepicker when calling can_move_king_or_pawn().
closes https://github.com/official-stockfish/Stockfish/pull/6088
bench: 2178135