Adding `intersperse` to the API

I would like to suggest the addition of `intersperse :: a -> Vector a -> Vector a` to the API.

I have a prototype that I reuse in my projects, that reads:

```haskell
intercalateVec :: Text -> Vector Text -> Vector Text
intercalateVec sep vector =
if V.null vector
then vector
else V.tail $ V.concatMap (\word -> V.fromList [sep, word]) vector
```

But I would be interested to know if a better implementation is possible.

Review the vector package's existing Vector API and the supplied intercalateVec prototype first. Determine the intended behavior of intersperse, including empty and non-empty vectors, and compare possible implementations before proposing the API addition. Completion should include an agreed implementation and validation of its behavior.

Written by the indexing model from the issue text.