With Float16 we need to differentiate b/w vector lane element type and carrier type. while element type corresponds to exact type of lane i.e. Float16.class carrier type corresponds to the storage type required to propagate IEEE 754 float16 values to inline expander.

Add a new carrier type to existing LaneType structure and use it for following purpose.
 - To compute preferred shape of vector.
 - To allocate vector backing storage during dummy vector and iota array creation.
 - Sanity checking to ensure vector lane type is a primitive type in inline expander.