Blend nnue complexity with classical.

Following mstembera's test of the complexity value derived from nnue values,
this change blends that idea with the old complexity calculation.

STC 10+0.1:
LLR: 2.95 (-2.94,2.94) <0.00,2.50>
Total: 42320 W: 11436 L: 11148 D: 19736
Ptnml(0-2): 209, 4585, 11263, 4915, 188
https://tests.stockfishchess.org/tests/live_elo/6295c9239c8c2fcb2bad7fd9

LTC 60+0.6:
LLR: 2.98 (-2.94,2.94) <0.50,3.00>
Total: 34600 W: 9393 L: 9125 D: 16082
Ptnml(0-2): 32, 3323, 10319, 3597, 29
https://tests.stockfishchess.org/tests/view/6295fd5d9c8c2fcb2bad88cf

closes https://github.com/official-stockfish/Stockfish/pull/4046

Bench 6078140

src/evaluate.h

@@ -44,7 +44,7 @@ namespace Eval {
   namespace NNUE {
 
     std::string trace(Position& pos);
-    Value evaluate(const Position& pos, bool adjusted = false);
+    Value evaluate(const Position& pos, bool adjusted = false, int* complexity = nullptr);
 
     void init();
     void verify();