Double extend more often via LMR

Double extend more often via LMR

Allow for first three moves always a two plies deeper LMR search.

STC:
LLR: 2.96 (-2.94,2.94) <-2.50,0.50>
Total: 206096 W: 51966 L: 52093 D: 102037
Ptnml(0-2): 664, 23817, 54293, 23530, 744
https://tests.stockfishchess.org/tests/view/616f197d40f619782fd4f75a

LTC:
LLR: 2.93 (-2.94,2.94) <-2.50,0.50>
Total: 62384 W: 15567 L: 15492 D: 31325
Ptnml(0-2): 40, 6633, 17777, 6696, 46
https://tests.stockfishchess.org/tests/view/616ffa1b4f0b65a0e231e682

closes https://github.com/official-stockfish/Stockfish/pull/3752

Bench: 6154836