general: Use deducation guides for std::lock_guard and std::unique_lock

Since C++17, the introduction of deduction guides for locking facilities
means that we no longer need to hardcode the mutex type into the locks
themselves, making it easier to switch mutex types, should it ever be
necessary in the future.

src/core/perf_stats.cpp

@@ -18,13 +18,13 @@ using std::chrono::microseconds;
 namespace Core {
 
 void PerfStats::BeginSystemFrame() {
-    std::lock_guard<std::mutex> lock(object_mutex);
+    std::lock_guard lock{object_mutex};
 
     frame_begin = Clock::now();
 }
 
 void PerfStats::EndSystemFrame() {
-    std::lock_guard<std::mutex> lock(object_mutex);
+    std::lock_guard lock{object_mutex};
 
     auto frame_end = Clock::now();
     accumulated_frametime += frame_end - frame_begin;
@@ -35,13 +35,13 @@ void PerfStats::EndSystemFrame() {
 }
 
 void PerfStats::EndGameFrame() {
-    std::lock_guard<std::mutex> lock(object_mutex);
+    std::lock_guard lock{object_mutex};
 
     game_frames += 1;
 }
 
 PerfStats::Results PerfStats::GetAndResetStats(microseconds current_system_time_us) {
-    std::lock_guard<std::mutex> lock(object_mutex);
+    std::lock_guard lock(object_mutex);
 
     const auto now = Clock::now();
     // Walltime elapsed since stats were reset
@@ -67,7 +67,7 @@ PerfStats::Results PerfStats::GetAndResetStats(microseconds current_system_time_
 }
 
 double PerfStats::GetLastFrameTimeScale() {
-    std::lock_guard<std::mutex> lock(object_mutex);
+    std::lock_guard lock{object_mutex};
 
     constexpr double FRAME_LENGTH = 1.0 / GPU::SCREEN_REFRESH_RATE;
     return duration_cast<DoubleSecs>(previous_frame_length).count() / FRAME_LENGTH;