refactor(go): optimize GoPsiUtil.getDeclarationName function

- Remove unnecessary imports and unused code.
- Simplify the logic of getting the declaration name.
- Improve readability and maintainability of the code.

Author: phodal

goland/src/main/kotlin/cc/unitmesh/go/context/GoStructContextBuilder.kt

@@ -2,6 +2,7 @@ package cc.unitmesh.go.context
 
 import cc.unitmesh.devti.context.ClassContext
 import cc.unitmesh.devti.context.builder.ClassContextBuilder
+import cc.unitmesh.go.util.GoPsiUtil
 import com.goide.psi.GoMethodDeclaration
 import com.goide.psi.GoTypeDeclaration
 import com.goide.psi.GoTypeSpec
@@ -27,13 +28,7 @@ class GoStructContextBuilder : ClassContextBuilder {
         val methods = methodPairs.map { it.first }
             .filterIsInstance<GoMethodDeclaration>()
 
-        val name = when (psiElement) {
-            is GoTypeSpec -> psiElement.name
-            is GoTypeDeclaration -> {
-                psiElement.typeSpecList.first().name
-            }
-            else -> null
-        }
+        val name = GoPsiUtil.getDeclarationName(psiElement)
 
         return ClassContext(
             psiElement, psiElement.text, name, methods, emptyList(), emptyList(), emptyList()

goland/src/main/kotlin/cc/unitmesh/go/context/GoVariableContextBuilder.kt

@@ -3,9 +3,7 @@ package cc.unitmesh.go.context
 import cc.unitmesh.devti.context.VariableContext
 import cc.unitmesh.devti.context.builder.VariableContextBuilder
 import com.goide.psi.GoVarOrConstDefinition
-import com.goide.psi.GoVarOrConstSpec
 import com.intellij.psi.PsiElement
-import com.intellij.psi.util.elementType
 
 class GoVariableContextBuilder : VariableContextBuilder {
     override fun getVariableContext(

goland/src/main/kotlin/cc/unitmesh/go/util/GoPsiUtil.kt

@@ -1,12 +1,20 @@
 package cc.unitmesh.go.util
 
-import com.goide.psi.GoFunctionOrMethodDeclaration
-import com.goide.psi.GoTypeList
-import com.goide.psi.GoTypeSpec
+import com.goide.psi.*
 import com.intellij.openapi.roots.ProjectFileIndex
 import com.intellij.psi.PsiElement
 
 object GoPsiUtil {
+    fun getDeclarationName(psiElement: PsiElement): String? {
+        return when (psiElement) {
+            is GoNamedElement -> psiElement.name
+            is GoTypeDeclaration -> psiElement.typeSpecList.singleOrNull()?.name
+            is GoVarOrConstDeclaration<*> -> (psiElement.specList.singleOrNull() as? GoVarOrConstSpec)?.definitionList?.singleOrNull()?.name
+            is GoVarOrConstSpec<*> -> psiElement.definitionList.singleOrNull()?.name
+            else -> null
+        }
+    }
+
     fun findRelatedTypes(declaration: GoFunctionOrMethodDeclaration): List<GoTypeSpec> {
         val signature = declaration.signature ?: return emptyList()