Replace std::lock_guard and std::lock with std::scoped_lock (#1758)

std::scoped_lock was introduced in C++17 and is strictly better than
std::lock_guard as it supports locking any number of mutexes safely.
It's also easier to use than std::lock for locking multiple mutexes at
once.

wpilibc/src/main/native/cpp/smartdashboard/SendableBase.cpp

@@ -34,22 +34,22 @@ SendableBase& SendableBase::operator=(SendableBase&& rhs) {
 }
 
 std::string SendableBase::GetName() const {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   return m_name;
 }
 
 void SendableBase::SetName(const wpi::Twine& name) {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   m_name = name.str();
 }
 
 std::string SendableBase::GetSubsystem() const {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   return m_subsystem;
 }
 
 void SendableBase::SetSubsystem(const wpi::Twine& subsystem) {
-  std::lock_guard lock(m_mutex);
+  std::scoped_lock lock(m_mutex);
   m_subsystem = subsystem.str();
 }