feat(java): include class inheritors in related classes lookup

Add support for finding class inheritors in JavaRelatedClassesProvider.
This enhances the lookup functionality by including inheritors in the
distinct list of related classes.

Author: phodal

java/src/main/kotlin/cc/unitmesh/idea/provider/JavaRelatedClassesProvider.kt

@@ -1,5 +1,6 @@
 package cc.unitmesh.idea.provider
 
+import cc.unitmesh.devti.mcp.Query
 import cc.unitmesh.devti.provider.RelatedClassesProvider
 import cc.unitmesh.idea.context.JavaContextCollection
 import cc.unitmesh.idea.service.JavaTypeUtil.resolveByType
@@ -9,10 +10,13 @@ import com.intellij.openapi.application.runReadAction
 import com.intellij.openapi.project.Project
 import com.intellij.openapi.roots.ProjectFileIndex
 import com.intellij.psi.*
+import com.intellij.psi.search.GlobalSearchScope
+import com.intellij.psi.search.searches.ClassInheritorsSearch
 import com.intellij.psi.util.PsiTreeUtil
 import com.intellij.psi.util.PsiUtil
 import com.intellij.testIntegration.TestFinderHelper
 
+
 class JavaRelatedClassesProvider : RelatedClassesProvider {
     override fun lookupIO(element: PsiElement): List<PsiClass> {
         return when (element) {
@@ -80,7 +84,12 @@ class JavaRelatedClassesProvider : RelatedClassesProvider {
                         else -> null
                     }
                 }
-                return@runReadAction (fieldsTypes + methods).distinct()
+                val inheritors: Collection<PsiClass> =
+                    ClassInheritorsSearch.search(clazz, GlobalSearchScope.allScope(clazz.project), true)
+                        .findAll()
+                        .toList()
+
+                return@runReadAction (fieldsTypes + methods + inheritors).distinct()
             }
         }?.get() ?: emptyList()
     }