Migrate UnlinkedParam.defaultValue to UnlinkedExecutable.bodyExpr.

pkg/analyzer/lib/src/summary/resynthesize.dart

Index: pkg/analyzer/lib/src/summary/resynthesize.dart
diff --git a/pkg/analyzer/lib/src/summary/resynthesize.dart b/pkg/analyzer/lib/src/summary/resynthesize.dart
index d0d4819279d16e3119a7551da04a7f4c67d77eb5..d8e3f2e23bf2b2dc141764a8c09e36f83942f0f2 100644
--- a/pkg/analyzer/lib/src/summary/resynthesize.dart
+++ b/pkg/analyzer/lib/src/summary/resynthesize.dart
@@ -2332,9 +2332,9 @@ class _UnitResynthesizer {
             new DefaultFieldFormalParameterElementImpl(
                 serializedParameter.name, nameOffset);
         initializingParameter = defaultParameter;
-        if (serializedParameter.defaultValue != null) {
+        if (serializedParameter.initializer?.bodyExpr != null) {
           defaultParameter.constantInitializer = _buildConstExpression(
-              enclosingElement, serializedParameter.defaultValue);
+              enclosingElement, serializedParameter.initializer.bodyExpr);
           defaultParameter.defaultValueCode =
               serializedParameter.defaultValueCode;
         }