gpui: Implement From<String> for ElementId (#44447)

Release Notes:

- N/A

## Before

```rs
div()
    .id(SharedString::from(format!("process-entry-{ix}-command")))
```

## After

```rs
div()
    .id(format!("process-entry-{ix}-command"))
```

crates/git_ui/src/stash_picker.rs

@@ -464,7 +464,7 @@ impl PickerDelegate for StashListDelegate {
             );
 
         Some(
-            ListItem::new(SharedString::from(format!("stash-{ix}")))
+            ListItem::new(format!("stash-{ix}"))
                 .inset(true)
                 .spacing(ListItemSpacing::Sparse)
                 .toggle_state(selected)