Various Benchmark Fixes for AzCore (#7611)

Fixed crash in Allocators Benchmark multithreaded test due to the HPHA schema not having proper multithread protection around the `mFreeTree` member in `tree_get_unused_memory` function.
The `mFreeTree intrusive set is able to modified on multiple threads.

Replaced the custom intrusive_list implementation n HPHA schema with AZStd::intrusive_list

Added a `ScopedAllocatorBenchmarkEnvironment` class to provide an RAI mechanism for initializing the SystemAllocator in Benchmark Test

Rermoved the `AzCoreBenchmarkEnvironment` in lieu of the `ScopedAllocatorBenchmarkEnvironment` class

Fixed assert when running Allocator Benchmarks in debug due to mismatch PauseTiming/ResumeTiming in Allocator Benchmark Fixtures

Added `ScopedRegisterBenchmarkEnvironment` RAII class to provide lifetime guarantees on BenchmarkEnvironments registered via the `AZ_UNIT_TEST_HOOK`

Initialized the intrusive_multiset_node members to nullptr in all build configurations instead of only debug as the cost negligible and it is useful for debugging.

fixes LYN-10210

Signed-off-by: lumberyard-employee-dm <56135373+lumberyard-employee-dm@users.noreply.github.com>

Code/Framework/AzCore/Tests/Main.cpp

@@ -7,29 +7,13 @@
  */
 
 #include <AzCore/UnitTest/UnitTest.h>
+#include <AzCore/UnitTest/TestTypes.h>
 #include <AzTest/AzTest.h>
-#include <AzCore/Memory/SystemAllocator.h>
 
 
 #if defined(HAVE_BENCHMARK)
 
-namespace AzCore
-{
-    class AzCoreBenchmarkEnvironment
-        : public AZ::Test::BenchmarkEnvironmentBase
-    {
-        void SetUpBenchmark() override
-        {
-            AZ::AllocatorInstance<AZ::SystemAllocator>::Create();
-        }
-        void TearDownBenchmark() override
-        {
-            AZ::AllocatorInstance<AZ::SystemAllocator>::Destroy();
-        }
-    };
-}
-
-AZ_UNIT_TEST_HOOK(DEFAULT_UNIT_TEST_ENV, AzCore::AzCoreBenchmarkEnvironment)
+AZ_UNIT_TEST_HOOK(DEFAULT_UNIT_TEST_ENV, UnitTest::ScopedAllocatorBenchmarkEnvironment)
 
 #else