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.

cscore/src/main/native/cpp/SinkImpl.h

@@ -48,7 +48,7 @@ class SinkImpl : public PropertyContainer {
   void SetSource(std::shared_ptr<SourceImpl> source);
 
   std::shared_ptr<SourceImpl> GetSource() const {
-    std::lock_guard lock(m_mutex);
+    std::scoped_lock lock(m_mutex);
     return m_source;
   }