AppCode:Debugger: do not show internal file types in UI (OC-3943)

platform/core-api/src/com/intellij/openapi/fileTypes/LanguageFileType.java

@@ -54,6 +54,13 @@ public abstract class LanguageFileType implements FileType{
 
   @Override
   public final boolean isReadOnly() {
+    return isSystem();
+  }
+
+  /**
+   * System file types cannot be editor and are not shown in the interface
+   */
+  protected boolean isSystem() {
     return false;
   }