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.

wpiutil/src/test/native/cpp/priority_mutex_test.cpp

@@ -32,7 +32,7 @@ class Notification {
   }
   // Sets the condition to true, and wakes all waiting threads.
   void Notify() {
-    std::lock_guard lock(m_mutex);
+    std::scoped_lock lock(m_mutex);
     m_set = true;
     m_condition.notify_all();
   }