Add a VectorCast function that safely casts from Vector<Offset<T>> to Vector<Offset<U>> if U is a base class of T.
Add a VectorCast function that safely casts from
Vector<Offset<T>> to Vector<Offset<U>> if U is a base
class of T.

This is useful for when you want to generically
iterate over a vector of objects that derive from
flatbuffers::Table.

Change-Id: I59161e3b9f40501f72e02b46509be9dc8ab86c6b

endorph-soft/flatbuffers,MiCHiLU/flatbuffers,evolutional/flatbuffers,chenkai036/flatbuffers,endorph-soft/flatbuffers,chenkai036/flatbuffers,MiCHiLU/flatbuffers,royalharsh/flatbuffers,endorph-soft/flatbuffers,chenkai036/flatbuffers,stewartmiles/flatbuffers,royalharsh/flatbuffers,chenkai036/flatbuffers,rw/flatbuffers,evolutional/flatbuffers,evolutional/flatbuffers,MiCHiLU/flatbuffers,chenkai036/flatbuffers,alexames/flatbuffers,jekinchen/flatjni,chenkai036/flatbuffers,hgl888/flatbuffers,hgl888/flatbuffers,royalharsh/flatbuffers,jasonstubbs/flatbuffers,google/flatbuffers,chenkai036/flatbuffers,hgl888/flatbuffers,jekinchen/flatjni,evolutional/flatbuffers,MiCHiLU/flatbuffers,alexames/flatbuffers,endorph-soft/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,jekinchen/flatjni,pjulien/flatbuffers,google/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,chenkai036/flatbuffers,jasonstubbs/flatbuffers,hgl888/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,MiCHiLU/flatbuffers,pjulien/flatbuffers,jasonstubbs/flatbuffers,jekinchen/flatjni,pjulien/flatbuffers,jasonstubbs/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,rw/flatbuffers,rw/flatbuffers,google/flatbuffers,evolutional/flatbuffers,MiCHiLU/flatbuffers,pjulien/flatbuffers,endorph-soft/flatbuffers,rw/flatbuffers,pjulien/flatbuffers,royalharsh/flatbuffers,rw/flatbuffers,alexames/flatbuffers,jasonstubbs/flatbuffers,hgl888/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,DavadDi/flatbuffers,google/flatbuffers,rw/flatbuffers,google/flatbuffers,DavadDi/flatbuffers,google/flatbuffers,stewartmiles/flatbuffers,evolutional/flatbuffers,google/flatbuffers,google/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,google/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,jasonstubbs/flatbuffers,evolutional/flatbuffers,MiCHiLU/flatbuffers,jekinchen/flatjni,jasonstubbs/flatbuffers,evolutional/flatbuffers,evolutional/flatbuffers,alexames/flatbuffers,google/flatbuffers,stewartmiles/flatbuffers,endorph-soft/flatbuffers,royalharsh/flatbuffers,MiCHiLU/flatbuffers,pjulien/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,jasonstubbs/flatbuffers,stewartmiles/flatbuffers,pjulien/flatbuffers,rw/flatbuffers,google/flatbuffers,endorph-soft/flatbuffers,pjulien/flatbuffers,rw/flatbuffers,jekinchen/flatjni,rw/flatbuffers,alexames/flatbuffers,DavadDi/flatbuffers,alexames/flatbuffers,jekinchen/flatjni,pjulien/flatbuffers,chenkai036/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,alexames/flatbuffers,google/flatbuffers,royalharsh/flatbuffers,endorph-soft/flatbuffers,jekinchen/flatjni,jekinchen/flatjni,endorph-soft/flatbuffers,DavadDi/flatbuffers,royalharsh/flatbuffers,rw/flatbuffers,stewartmiles/flatbuffers,rw/flatbuffers,royalharsh/flatbuffers,jekinchen/flatjni,hgl888/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,DavadDi/flatbuffers,pjulien/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,google/flatbuffers,DavadDi/flatbuffers,chenkai036/flatbuffers