[LYN-3548] Change IMGUI to use list of levels with prefab LoadLevel instead of text box

There was an intermittent crash related to garbage in the level name box with prefabs, possibly due to levelName being uninitialized.  This change improves the UX by listing out all the possible choices, instead of making people type it in.

Gems/ImGui/Code/Source/LYCommonMenu/ImGuiLYCommonMenu.cpp

@@ -15,6 +15,7 @@
 
 #ifdef IMGUI_ENABLED
 #include <AzCore/std/string/conversions.h>
+#include <AzCore/std/sort.h>
 #include <AzFramework/Input/Buses/Requests/InputSystemCursorRequestBus.h>
 #include <AzFramework/Input/Devices/Mouse/InputDeviceMouse.h>
 #include <ILevelSystem.h>
@@ -251,15 +252,37 @@ namespace ImGui
 
                     if (usePrefabSystemForLevels)
                     {
-                        char levelName[256];
+                        // Run through all the assets in the asset catalog and gather up the list of level assets
+
+                        AZ::Data::AssetType levelAssetType = lvlSystem->GetLevelAssetType();
+                        AZStd::vector<AZStd::string> levelNames;
+                        auto enumerateCB =
+                            [levelAssetType, &levelNames]([[maybe_unused]] const AZ::Data::AssetId id, const AZ::Data::AssetInfo& assetInfo)
+                        {
+                            if (assetInfo.m_assetType == levelAssetType)
+                            {
+                                levelNames.emplace_back(assetInfo.m_relativePath);
+                            }
+                        };
+
+                        AZ::Data::AssetCatalogRequestBus::Broadcast(
+                            &AZ::Data::AssetCatalogRequestBus::Events::EnumerateAssets, nullptr, enumerateCB, nullptr);
+
+                        AZStd::sort(levelNames.begin(), levelNames.end());
+
+                        // Create a menu item for each level asset, with an action to load it if selected.
+
                         ImGui::TextColored(ImGui::Colors::s_PlainLabelColor, "Load Level: ");
-                        bool result = ImGui::InputText("", levelName, sizeof(levelName), ImGuiInputTextFlags_EnterReturnsTrue);
-                        if (result)
+                        for (int i = 0; i < levelNames.size(); i++)
                         {
-                            AZ_TracePrintf("Imgui", "Attempting to load level '%s'\n", levelName);
-                            AZ::TickBus::QueueFunction([lvlSystem, levelName]() {
-                                lvlSystem->LoadLevel(levelName);
-                            });
+                            if (ImGui::MenuItem(AZStd::string::format("%d- %s", i, levelNames[i].c_str()).c_str()))
+                            {
+                                AZ::TickBus::QueueFunction(
+                                    [lvlSystem, levelNames, i]()
+                                    {
+                                        lvlSystem->LoadLevel(levelNames[i].c_str());
+                                    });
+                            }
                         }
                     }
                     else
@@ -269,9 +292,8 @@ namespace ImGui
                         {
                             if (ImGui::MenuItem(AZStd::string::format("%d- %s", i, lvlSystem->GetLevelInfo(i)->GetName()).c_str()))
                             {
-                                AZStd::string mapCommandString = AZStd::string::format("map %s", lvlSystem->GetLevelInfo(i)->GetName());
-                                AZ::TickBus::QueueFunction([mapCommandString]() {
-                                    gEnv->pConsole->ExecuteString(mapCommandString.c_str());
+                                AZ::TickBus::QueueFunction([lvlSystem, i]() {
+                                    lvlSystem->LoadLevel(lvlSystem->GetLevelInfo(i)->GetName());
                                 });
                             }
                         }