[VFABI] Create FunctionType for vector functions (#75058)

`createFunctionType` returns a FunctionType  that may contain a mask,
which is currently placed as the last parameter to the Function.
The placement happens according to `VFParameters` of `VFInfo`, and it
should be able to handle VFABI specification changes.

Regarding the return type, it uses the scalar type of the input instruction,
as the specification does not encode in the mangled name such information.
If that ever happens, that information should be available from `VFInfo`.