[CQ] remove unused imports (flutter#8488)

Import cleanup and a few wildcard import fixes.

---

<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](flutter#8098)).
</details>

Author: pq

src/io/flutter/devtools/AbstractDevToolsViewFactory.java

@@ -11,7 +11,6 @@
 import com.intellij.openapi.wm.ToolWindowFactory;
 import com.intellij.openapi.wm.ex.ToolWindowManagerListener;
 import com.intellij.util.messages.MessageBusConnection;
-import icons.FlutterIcons;
 import io.flutter.FlutterUtils;
 import io.flutter.actions.RefreshToolWindowAction;
 import io.flutter.run.daemon.DevToolsInstance;
@@ -26,7 +25,7 @@
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import javax.swing.Icon;
+import javax.swing.*;
 import java.util.List;
 import java.util.Optional;
 
@@ -157,7 +156,8 @@ private void loadDevToolsInEmbeddedBrowser(@NotNull Project project,
               FlutterUtils.embeddedBrowser(project))
             .ifPresent(embeddedBrowser ->
                        {
-                         embeddedBrowser.openPanel(toolWindow, getToolWindowTitle(), getToolWindowIcon(), devToolsUrl, System.out::println, warningMessage);
+                         embeddedBrowser.openPanel(toolWindow, getToolWindowTitle(), getToolWindowIcon(), devToolsUrl, System.out::println,
+                                                   warningMessage);
                          devToolsLoadedInBrowser = true;
                          doAfterBrowserOpened(project, embeddedBrowser);
                          // The "refresh" action refreshes the embedded browser, not the panel.

src/io/flutter/view/EmbeddedBrowser.java

@@ -16,7 +16,6 @@
 import com.intellij.ui.content.Content;
 import com.intellij.ui.content.ContentManager;
 import com.intellij.util.ui.JBUI;
-import icons.FlutterIcons;
 import io.flutter.devtools.DevToolsUrl;
 import io.flutter.utils.AsyncUtils;
 import io.flutter.utils.LabelInput;
@@ -26,8 +25,11 @@
 
 import javax.swing.*;
 import java.awt.*;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Consumer;