[wpilibc] Shuffleboard SimpleWidget: Return pointer instead of reference (#4703)

Based on beta test feedback, returning a pointer is more intuitive, as
typically the return value is late bound to an instance variable.

wpilibc/src/main/native/cpp/shuffleboard/ShuffleboardContainer.cpp

@@ -83,7 +83,7 @@ SimpleWidget& ShuffleboardContainer::Add(std::string_view title,
   auto ptr = widget.get();
   m_components.emplace_back(std::move(widget));
   ptr->GetEntry(nt::GetStringFromType(defaultValue.type()))
-      .SetDefault(defaultValue);
+      ->SetDefault(defaultValue);
   return *ptr;
 }
 
@@ -322,7 +322,7 @@ SimpleWidget& ShuffleboardContainer::AddPersistent(
     std::string_view title, const nt::Value& defaultValue) {
   auto& widget = Add(title, defaultValue);
   widget.GetEntry(nt::GetStringFromType(defaultValue.type()))
-      .GetTopic()
+      ->GetTopic()
       .SetPersistent(true);
   return widget;
 }

wpilibc/src/main/native/cpp/shuffleboard/SimpleWidget.cpp

@@ -14,19 +14,19 @@ SimpleWidget::SimpleWidget(ShuffleboardContainer& parent,
                            std::string_view title)
     : ShuffleboardValue(title), ShuffleboardWidget(parent, title), m_entry() {}
 
-nt::GenericEntry& SimpleWidget::GetEntry() {
+nt::GenericEntry* SimpleWidget::GetEntry() {
   if (!m_entry) {
     ForceGenerate();
   }
-  return m_entry;
+  return &m_entry;
 }
 
-nt::GenericEntry& SimpleWidget::GetEntry(std::string_view typeString) {
+nt::GenericEntry* SimpleWidget::GetEntry(std::string_view typeString) {
   if (!m_entry) {
     m_typeString = typeString;
     ForceGenerate();
   }
-  return m_entry;
+  return &m_entry;
 }
 
 void SimpleWidget::BuildInto(std::shared_ptr<nt::NetworkTable> parentTable,