PythonProxyNotificationHandler::OnEventGenericHook acquires the Python GIL before executing (#3904)

- Protected python execution of OnEventGenericHook by trying to lock the GIL and show a descriptive error when it was not possible to lock.
- Improved mechanism to lock python mutex and GIL in PhytonSystemComponent. Acquiring/releasing GIL once per thread.
- Added unit test to verify errors are fired when trying to execute OnEventGenericHook from another thread (as it should not able to acquire the GIL).
- Improved python threading tests to actually using python buses.

Signed-off-by: moraaar moraaar@amazon.com

Gems/EditorPythonBindings/Code/Tests/PythonTraceMessageSink.h

@@ -37,6 +37,15 @@ namespace UnitTest
         using EvaluationMap = AZStd::unordered_map<int, int>; // tag to count
         EvaluationMap m_evaluationMap;
 
+        AZStd::mutex m_lock;
+
+        void CleanUp()
+        {
+            AZStd::lock_guard<decltype(m_lock)> lock(m_lock);
+            m_evaluateMessage = {};
+            m_evaluationMap.clear();
+        }
+
         //////////////////////////////////////////////////////////////////////////
         // TraceMessageDrillerBus
         void OnPrintf(const char* window, const char* message) override
@@ -46,6 +55,8 @@ namespace UnitTest
 
         void OnOutput(const char* window, const char* message) override
         {
+            AZStd::lock_guard<decltype(m_lock)> lock(m_lock);
+
             if (m_evaluateMessage)
             {
                 int key = m_evaluateMessage(window, message);