Fix visibility of default Builder constructors

Author: kstich

smithy-model/src/main/java/software/amazon/smithy/model/shapes/OperationShape.java

@@ -210,7 +210,7 @@ public static final class Builder extends AbstractShapeBuilder<Builder, Operatio
         private ShapeId output = UnitTypeTrait.UNIT;
         private final BuilderRef<Set<ShapeId>> errors = BuilderRef.forOrderedSet();
 
-        private Builder() {}
+        public Builder() {}
 
         private Builder(OperationShape shape) {
             shape.updateBuilder(this);

smithy-model/src/main/java/software/amazon/smithy/model/shapes/ResourceShape.java

@@ -220,7 +220,7 @@ public static final class Builder extends EntityShape.Builder<Builder, ResourceS
         private ShapeId delete;
         private ShapeId list;
 
-        private Builder() {}
+        public Builder() {}
 
         private Builder(ResourceShape shape) {
             shape.updateBuilder(this);