Add ability to display backgrounds for inlay hints (#18010)

This PR adds the ability to display backgrounds for inlay hints within
the editor.

This is controlled by the new `inlay_hints.show_background` setting.
This setting defaults to `false`.

To enable the setting, add the following to your `settings.json`:

```json
{
  "inlay_hints": {
    "enabled": true,
    "show_background": true
  }
}
```

When enabled, the inlay hint backgrounds will use the `hint.background`
color from the theme.

| Disabled | Enabled |
|
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|
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|
| <img width="1624" alt="Screenshot 2024-09-17 at 4 21 53 PM"
src="https://github.com/user-attachments/assets/5534d09b-1e22-4c6f-9d82-314796ed7d22">
| <img width="1624" alt="Screenshot 2024-09-17 at 4 21 43 PM"
src="https://github.com/user-attachments/assets/6ec58cde-6115-4db4-be95-97c5f2f54b2d">
|

Related issues:

- #12485
- #17392

Release Notes:

- Added an `inlay_hints.show_background` setting to allow displaying
backgrounds for inlay hints in the editor.
  - This setting defaults to `false`.
- If enabled, the inlay hint backgrounds will use the `hint.background`
color from the theme.

crates/editor/src/editor.rs

@@ -412,6 +412,19 @@ impl Default for EditorStyle {
     }
 }
 
+pub fn make_inlay_hints_style(cx: &WindowContext) -> HighlightStyle {
+    let show_background = all_language_settings(None, cx)
+        .language(None)
+        .inlay_hints
+        .show_background;
+
+    HighlightStyle {
+        color: Some(cx.theme().status().hint),
+        background_color: show_background.then(|| cx.theme().status().hint_background),
+        ..HighlightStyle::default()
+    }
+}
+
 type CompletionId = usize;
 
 #[derive(Clone, Debug)]
@@ -10034,9 +10047,8 @@ impl Editor {
                                                 syntax: cx.editor_style.syntax.clone(),
                                                 status: cx.editor_style.status.clone(),
                                                 inlay_hints_style: HighlightStyle {
-                                                    color: Some(cx.theme().status().hint),
                                                     font_weight: Some(FontWeight::BOLD),
-                                                    ..HighlightStyle::default()
+                                                    ..make_inlay_hints_style(cx)
                                                 },
                                                 suggestions_style: HighlightStyle {
                                                     color: Some(cx.theme().status().predictive),
@@ -12992,10 +13004,7 @@ impl Render for Editor {
                 scrollbar_width: EditorElement::SCROLLBAR_WIDTH,
                 syntax: cx.theme().syntax().clone(),
                 status: cx.theme().status().clone(),
-                inlay_hints_style: HighlightStyle {
-                    color: Some(cx.theme().status().hint),
-                    ..HighlightStyle::default()
-                },
+                inlay_hints_style: make_inlay_hints_style(cx),
                 suggestions_style: HighlightStyle {
                     color: Some(cx.theme().status().predictive),
                     ..HighlightStyle::default()