Consider side to move advantage for nonpawn piece threats

[TheRealGioviok]

Passed STC:

Test  | stmthreats1
Elo   | 2.02 +- 1.61 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 2.98 (-2.94, 2.94) [0.00, 3.00]
Games | N: 62160 W: 16556 L: 16194 D: 29410
Penta | [837, 7313, 14400, 7711, 819]

https://ob.cwchess.org/test/1550/

Passed LTC:

Test  | stmthreats1
Elo   | 2.43 +- 1.84 (95%)
SPRT  | 40.0+0.40s Threads=1 Hash=64MB
LLR   | 2.96 (-2.94, 2.94) [0.00, 3.00]
Games | N: 38752 W: 9694 L: 9423 D: 19635
Penta | [181, 4591, 9592, 4800, 212]

https://ob.cwchess.org/test/1554/

Bench: 12449231