ATOM-13791 Editor: ImGui profiling tools doesn't work correctly due to disabled RenderPipelines

- Added pause/resume button to ImGui Profiler to pause/resume profiling
- Added showing pass execution timeline
- Change TimestampResult to include both begin tick and duration tick. Update some function names of TimestampResult.
- Update some functions names in Pass.
- Stop showing accumulated time for ParentPass.
- Fixed a crash issue with ImGuiManager which doesn't have default font.

Gems/ImGui/Code/Source/ImGuiManager.cpp

@@ -222,6 +222,10 @@ void ImGuiManager::Initialize()
     io.DisplaySize.x = 1920;
     io.DisplaySize.y = 1080;
 
+    // Create a default font
+    io.Fonts->AddFontDefault();
+    io.Fonts->Build();
+
     // Broadcast ImGui Ready to Listeners
     ImGuiUpdateListenerBus::Broadcast(&IImGuiUpdateListener::OnImGuiInitialize);
     m_currentControllerIndex = -1;