[CQ] prefer “magic” flow layout constants (#8194)

`VerticalFlowAlignment` identifies some "magic" constants:


![image](https://github.com/user-attachments/assets/d49fa227-d381-4cf3-867d-17db1c5fe1c5)

that are prefered:


![image](https://github.com/user-attachments/assets/8c852821-d863-4d27-8723-b91fe260731b)

(Note that both `CENTER` and `MIDDLE` are initialized to `1` so this is
semantics preserving.)



---

- [x] I’ve reviewed the contributor guide and applied the relevant
portions to this PR.

<details>
  <summary>Contribution guidelines:</summary><br>

- See our [contributor
guide]([https://github.com/dart-lang/sdk/blob/main/CONTRIBUTING.md](https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview)
for general expectations for PRs.
- Larger or significant changes should be discussed in an issue before
creating a PR.
- Dart contributions to our repos should follow the [Dart style
guide](https://dart.dev/guides/language/effective-dart) and use `dart
format`.
- Java and Kotlin contributions should strive to follow Java and Kotlin
best practices
([discussion](#8098)).
</details>

Author: pq

flutter-idea/src/io/flutter/view/EmbeddedBrowser.java

@@ -200,7 +200,7 @@ protected void showLabels(List<LabelInput> labels, ContentManager contentManager
       }
     }
 
-    final JPanel center = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.CENTER));
+    final JPanel center = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.MIDDLE));
     center.add(panel);
     replacePanelLabel(center, contentManager);
   }

flutter-idea/src/io/flutter/view/ViewUtils.java

@@ -47,7 +47,7 @@ public void presentLabels(@NotNull ToolWindow toolWindow, @NotNull List<String>
     }
 
     // Use VerticalFlowLayout to center the block of labels vertically
-    final JPanel centerPanel = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.CENTER));
+    final JPanel centerPanel = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.MIDDLE));
     centerPanel.add(labelsPanel);
 
     replacePanelLabel(toolWindow, centerPanel);
@@ -73,7 +73,7 @@ public void presentClickableLabel(ToolWindow toolWindow, List<LabelInput> labels
       }
     }
 
-    final JPanel center = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.CENTER));
+    final JPanel center = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.MIDDLE));
     center.add(panel);
     replacePanelLabel(toolWindow, center);
   }