dynamite: reimplement default values

Signed-off-by: Nikolas Rimikis <rimikis.nikolas@gmail.com>

packages/dynamite/lib/src/openapi_builder.dart

@@ -1472,6 +1472,53 @@ TypeResult resolveObject(
                   ..type = MethodType.getter,
               ),
             ]);
+
+          final defaults = <String>[];
+          for (final propertyName in schema.properties!.keys) {
+            final propertySchema = schema.properties![propertyName]!;
+            if (propertySchema.default_ != null) {
+              final value = propertySchema.default_!.toString();
+              final result = resolveType(
+                spec,
+                state,
+                propertySchema.type!,
+                propertySchema,
+              );
+              defaults.add('..${_toDartName(propertyName)} = ${_valueToEscapedValue(result, value)}');
+            }
+          }
+          if (defaults.isNotEmpty) {
+            b.methods.add(
+              Method(
+                (final b) => b
+                  ..name = '_defaults'
+                  ..returns = refer('void')
+                  ..static = true
+                  ..lambda = true
+                  ..annotations.add(
+                    refer('BuiltValueHook').call(
+                      [],
+                      {
+                        'initializeBuilder': refer('true'),
+                      },
+                    ),
+                  )
+                  ..requiredParameters.add(
+                    Parameter(
+                      (final b) => b
+                        ..name = 'b'
+                        ..type = refer('${state.prefix}${identifier}Builder'),
+                    ),
+                  )
+                  ..body = Code(
+                    <String?>[
+                      'b',
+                      ...defaults,
+                    ].join(),
+                  ),
+              ),
+            );
+          }
         },
       ),
     );