pub fn iter_mut(&mut self) -> ValueIterMut<'_, VE> {
        ValueIterMut {
            inner: self.inner.iter_mut(),
            phantom: PhantomData,
        }
    }
Returns an iterator mutably visiting all values associated with the
entry.

Values are iterated in insertion order.

# Examples

```
# use tonic::metadata::*;
let mut map = MetadataMap::default();
map.insert("host", "world".parse().unwrap());
map.append("host", "earth".parse().unwrap());

if let Entry::Occupied(mut e) = map.entry("host").unwrap() {
for e in e.iter_mut() {
e.set_sensitive(true);
}
}

let mut values = map.get_all("host");
let mut i = values.iter();
assert!(i.next().unwrap().is_sensitive());
assert!(i.next().unwrap().is_sensitive());
```
tonic/src/metadata/map.rs