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/inlay_hint_cache.rs

@@ -1296,6 +1296,7 @@ pub mod tests {
                 show_type_hints: allowed_hint_kinds.contains(&Some(InlayHintKind::Type)),
                 show_parameter_hints: allowed_hint_kinds.contains(&Some(InlayHintKind::Parameter)),
                 show_other_hints: allowed_hint_kinds.contains(&None),
+                show_background: false,
             })
         });
 
@@ -1428,6 +1429,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -1547,6 +1549,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -1777,6 +1780,7 @@ pub mod tests {
                 show_type_hints: allowed_hint_kinds.contains(&Some(InlayHintKind::Type)),
                 show_parameter_hints: allowed_hint_kinds.contains(&Some(InlayHintKind::Parameter)),
                 show_other_hints: allowed_hint_kinds.contains(&None),
+                show_background: false,
             })
         });
 
@@ -1941,6 +1945,7 @@ pub mod tests {
                     show_parameter_hints: new_allowed_hint_kinds
                         .contains(&Some(InlayHintKind::Parameter)),
                     show_other_hints: new_allowed_hint_kinds.contains(&None),
+                    show_background: false,
                 })
             });
             cx.executor().run_until_parked();
@@ -1987,6 +1992,7 @@ pub mod tests {
                 show_parameter_hints: another_allowed_hint_kinds
                     .contains(&Some(InlayHintKind::Parameter)),
                 show_other_hints: another_allowed_hint_kinds.contains(&None),
+                show_background: false,
             })
         });
         cx.executor().run_until_parked();
@@ -2047,6 +2053,7 @@ pub mod tests {
                 show_parameter_hints: final_allowed_hint_kinds
                     .contains(&Some(InlayHintKind::Parameter)),
                 show_other_hints: final_allowed_hint_kinds.contains(&None),
+                show_background: false,
             })
         });
         cx.executor().run_until_parked();
@@ -2122,6 +2129,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -2256,6 +2264,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -2551,6 +2560,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -2902,6 +2912,7 @@ pub mod tests {
                 show_type_hints: false,
                 show_parameter_hints: false,
                 show_other_hints: false,
+                show_background: false,
             })
         });
 
@@ -3096,6 +3107,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
         cx.executor().run_until_parked();
@@ -3131,6 +3143,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -3225,6 +3238,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
 
@@ -3305,6 +3319,7 @@ pub mod tests {
                 show_type_hints: true,
                 show_parameter_hints: true,
                 show_other_hints: true,
+                show_background: false,
             })
         });
         cx.executor().run_until_parked();