Add KernelToElementMap.getSpannable to avoid most usage of KernelAstAdapter.getNode

pkg/compiler/lib/src/kernel/element_map_impl.dart

Index: pkg/compiler/lib/src/kernel/element_map_impl.dart
diff --git a/pkg/compiler/lib/src/kernel/element_map_impl.dart b/pkg/compiler/lib/src/kernel/element_map_impl.dart
index f39c7050c08581a174fb38f1d506e9e989806e05..1bf6220f785493cdb51032da9628b41826cf7e98 100644
--- a/pkg/compiler/lib/src/kernel/element_map_impl.dart
+++ b/pkg/compiler/lib/src/kernel/element_map_impl.dart
@@ -680,6 +680,11 @@ class KernelToElementMapImpl extends KernelToElementMapMixin {
   ResolutionImpact computeWorldImpact(KMember member) {
     return _memberList[member.memberIndex].getWorldImpact(this);
   }
+
+  @override
+  Spannable getSpannable(MemberEntity member, ir.Node node) {
+    return member;
+  }
 }
 
 /// Environment for fast lookup of program libraries.