[verifier] migrate off to-be-removed PluginId.findId API (#8775)

https://github.com/JetBrains/intellij-community/blob/master/platform/extensions/src/com/intellij/openapi/extensions/PluginId.kt

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See: #8764

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Author: pq

src/io/flutter/FlutterUtils.java

@@ -349,7 +349,7 @@ public static boolean isXcodeWorkspaceFileName(@NotNull String name) {
 
   @NotNull
   public static PluginId getPluginId() {
-    final PluginId pluginId = PluginId.findId("io.flutter", "");
+    final PluginId pluginId = PluginId.getId("io.flutter");
     assert pluginId != null;
     return pluginId;
   }