Improve error message for unused type (#23633)

src/compiler/checker.ts

@@ -22183,7 +22183,8 @@ namespace ts {
             }
 
             if (!isRemovedPropertyFromObjectSpread(node.kind === SyntaxKind.Identifier ? node.parent : node)) {
-                addDiagnostic(UnusedKind.Local, createDiagnosticForNodeSpan(getSourceFileOfNode(declaration), declaration, node, Diagnostics._0_is_declared_but_its_value_is_never_read, name));
+                const message = isTypeDeclaration(declaration) ? Diagnostics._0_is_declared_but_never_used : Diagnostics._0_is_declared_but_its_value_is_never_read;
+                addDiagnostic(UnusedKind.Local, createDiagnosticForNodeSpan(getSourceFileOfNode(declaration), declaration, node, message, name));
             }
         }
 

src/compiler/diagnosticMessages.json

@@ -3530,6 +3530,11 @@
         "category": "Message",
         "code": 6195
     },
+    "'{0}' is declared but never used.": {
+        "category": "Error",
+        "code": 6196,
+        "reportsUnnecessary": true
+    },
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005

src/services/codefixes/fixUnusedIdentifier.ts

@@ -5,6 +5,7 @@ namespace ts.codefix {
     const fixIdDelete = "unusedIdentifier_delete";
     const errorCodes = [
         Diagnostics._0_is_declared_but_its_value_is_never_read.code,
+        Diagnostics._0_is_declared_but_never_used.code,
         Diagnostics.Property_0_is_declared_but_its_value_is_never_read.code,
         Diagnostics.All_imports_in_import_declaration_are_unused.code,
     ];