w.i.p New BVR AI: not cranking nor dropping altitude when facing a 2 ships flight. Only defending once enemy missiles go active.

[Mad_Shell]

Ran some tests, and here are the results:

- 1 vs 1: the AI cranks and drops altitude just after firing its missile (correct behaviour)

- 1 (blue) vs 2 (reds): each red AI fire a missile then cranks and dives. The blue AI launches 2 missiles, but stays nose hot and only defends once enemy missiles go active (track bug_BVr_AI_1vs2.trk)

- 2 (blues) vs 2 (reds): each red fires a missile against an enemy plane, and remains nose hot, only defending once enemy missile goes active. Same for blues. (track bug_BVr_AI_2vs2.trk)

bug_BVR_AI_1vs2.trk bug_BVR_AI_2vs2.trk

[BIGNEWY]

Thanks we are aware, the BVR work was for singletons first and groups will come later.