[Base] Add chrono support

- WinSystemClock is a FILETIME clock without scaling, can convert to
  system_time
- XSystemClock is a FILTETIME clock with scaling applied, can only
  convert to WinSystemClock

src/xenia/base/clock.h

@@ -2,7 +2,7 @@
  ******************************************************************************
  * Xenia : Xbox 360 Emulator Research Project                                 *
  ******************************************************************************
- * Copyright 2019 Ben Vanik. All rights reserved.                             *
+ * Copyright 2022 Ben Vanik. All rights reserved.                             *
  * Released under the BSD license - see LICENSE in the root for more details. *
  ******************************************************************************
  */
@@ -10,6 +10,7 @@
 #ifndef XENIA_BASE_CLOCK_H_
 #define XENIA_BASE_CLOCK_H_
 
+#include <chrono>
 #include <cstdint>
 
 #include "xenia/base/cvar.h"
@@ -24,6 +25,8 @@ DECLARE_bool(clock_source_raw);
 
 namespace xe {
 
+// chrono APIs in xenia/base/chrono.h are preferred
+
 class Clock {
  public:
   // Host ticks-per-second. Generally QueryHostTickFrequency should be used.