[analyzer] Resolve annotations on local variable elements

Metadata is attached to a `VariableDeclarationList`, not the individual
declarations therein.
Even though annotations from the list are copied down into the local
variable elements, the resolver did not set the `element` property on
those annotations which is required for computing the constant value in
a later step.
This is fixed by making the resolver visit the declaration list instead
of individual declarations.

Closes dart-lang#47502

Change-Id: Id6e47e6fa878e61be5279fa4127262deb73ab1c1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/217363
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/src/generated/element_resolver.dart

@@ -499,7 +499,7 @@ class ElementResolver extends SimpleAstVisitor<void> {
   }
 
   @override
-  void visitVariableDeclaration(VariableDeclaration node) {
+  void visitVariableDeclarationList(VariableDeclarationList node) {
     _resolveAnnotations(node.metadata);
   }
 

pkg/analyzer/test/src/dart/resolution/metadata_test.dart

@@ -151,6 +151,46 @@ A
 ''');
   }
 
+  test_onLocalVariable() async {
+    await assertNoErrorsInCode(r'''
+class A {
+  final int a;
+  const A(this.a);
+}
+
+void f() {
+  @A(3)
+  int? x;
+  print(x);
+}
+''');
+
+    var annotation = findNode.annotation('@A');
+    _assertResolvedNodeText(annotation, '''
+Annotation
+  arguments: ArgumentList
+    arguments
+      IntegerLiteral
+        literal: 3
+        staticType: int
+    leftParenthesis: (
+    rightParenthesis: )
+  atSign: @
+  element: self::@class::A::@constructor::•
+  name: SimpleIdentifier
+    staticElement: self::@class::A
+    staticType: null
+    token: A
+''');
+
+    final localVariable = findElement.localVar('x');
+    final annotationOnElement = localVariable.metadata.single;
+    _assertElementAnnotationValueText(annotationOnElement, '''
+A
+  a: int 3
+''');
+  }
+
   test_optIn_fromOptOut_class() async {
     newFile('$testPackageLibPath/a.dart', content: r'''
 class A {