Give us a proper inertial separator variable+event

Ideas
1

We currently have two un-settable local variables:
XMLVAR_InertSep1_Deployment
XMLVAR_InertSep1_Active

No more workarounds of using:
A:GENERAL ENG ANTI ICE POSITION
A:RECIP ENG ALTERNATE AIR POSITION
K:ANTI_ICE_GRADUAL_SET_ENGx