Adding sTGC strip efficiency.
Efficiency is computed per layer in each multiplet for the strip channel.
Three cases are considered:
Fully efficient case (4/4), where hits in all layers of each multiplet are verified.
Non efficient case (3/4), where 3 out 4 hits are verified in each multiplet.
Non efficient case (2/4), where 2 out 4 hit are verified in each multiplet.
In the non efficient case 2 layers are taken (reference layers) to compute a straight line equation for a segment traversing the multiplet, which is used to compute the hit position (global coordinates) of the missing layers (probe layers).