[Variant] `impl FromIterator` fpr `VariantPath`

Should it also `impl FromIterator` so people can do:
```rust
VariantPath::from_iter(["foo".into(), 0.into()])
```
or
```rust
["foo".into(), 0.into()].into_iter().collect::<VariantPath>()
```

_Originally posted by @scovich in https://github.com/apache/arrow-rs/pull/7942#discussion_r2213970123_
            