[development] Migrate Atom CPU timing stats tracking to use global stats profiler (#4549)

This change is a preparation for moving the CPU profiler/visualization system from Atom into its own Gem by removing the dependency on local time tracking object AZ::RHI::CpuTimingStatistics

Full changes include:
- Removed all usage of AZ::RHI::CpuTimingStatistics
-- Replaced with pushing to AZ::Statistics::StatisticalProfilerProxy global instance
- Promoted VariableTimer from AZ::RHI to AZ::Debug
- Removed now unused CpuTimingStatistics.h

Signed-off-by: AMZN-ScottR 24445312+AMZN-ScottR@users.noreply.github.com

Code/Framework/AzCore/AzCore/Debug/Timer.h

@@ -46,5 +46,23 @@ namespace AZ
         private:
             AZStd::sys_time_t m_timeStamp;
         };
+
+        //! Utility type that updates the given variable with the lifetime of the object in cycles.
+        //! Useful for quick scope based timing.
+        struct ScopedTimer
+        {
+            explicit ScopedTimer(AZStd::sys_time_t& variable)
+                : m_variable(variable)
+            {
+                m_timer.Stamp();
+            }
+            ~ScopedTimer()
+            {
+                m_variable = m_timer.GetDeltaTimeInTicks();
+            }
+
+            AZStd::sys_time_t& m_variable;
+            Timer m_timer;
+        };
     }
 }