Support for nested slice conversions (#1121)

This set of changes enables conversions for singly-nested slices. Multiple nesting hierarchies are only partially supported at this point. Conversion is also significantly more deterministic, which makes it easier to convert single slices without needing to reconvert every slice or level that relies on it as well.
Changes:

- Added version of Instance::AddInstance() that takes in an alias to allow for deterministic aliases
- Added a "SliceConverterEditorEntityContextComponent" that's used to specifically disable entity activation on creation. The disabling is done this way vs adding a new public API, because the disable shouldn't be required in any normal case outside of this tool.
- Disabled more AWS gems for the SliceConverter, as they're unneeded and cause issues if they're around in the tool.
- Added a small null check to the Camera Controller.
- Added the actual support for slice instance conversion. This instantiates the entities, applies the data patches, turns them into a prefab instance, and generates a JSON patch out of the changes.

Code/Tools/SerializeContextTools/Application.cpp

@@ -17,6 +17,7 @@
 #include <AzCore/Utils/Utils.h>
 
 #include <AzToolsFramework/Thumbnails/ThumbnailerNullComponent.h>
+#include <SliceConverterEditorEntityContextComponent.h>
 
 namespace AZ
 {
@@ -34,6 +35,9 @@ namespace AZ
         Application::Application(int argc, char** argv)
             : AzToolsFramework::ToolsApplication(&argc, &argv)
         {
+            // We need a specialized variant of EditorEntityContextCompnent for the SliceConverter, so we register the descriptor here.
+            RegisterComponentDescriptor(AzToolsFramework::SliceConverterEditorEntityContextComponent::CreateDescriptor());
+
             AZ::IO::FixedMaxPath projectPath = AZ::Utils::GetProjectPath();
             if (projectPath.empty())
             {
@@ -110,10 +114,21 @@ namespace AZ
 
         AZ::ComponentTypeList Application::GetRequiredSystemComponents() const
         {
-            // Use all of the default system components, but also add in the ThumbnailerNullComponent so that components requiring
-            // a ThumbnailService can still be started up.
+            // By default, we use all of the standard system components.
             AZ::ComponentTypeList components = AzToolsFramework::ToolsApplication::GetRequiredSystemComponents();
+
+            // Also add in the ThumbnailerNullComponent so that components requiring a ThumbnailService can still be started up.
             components.emplace_back(azrtti_typeid<AzToolsFramework::Thumbnailer::ThumbnailerNullComponent>());
+
+            // The Slice Converter requires a specialized variant of the EditorEntityContextComponent that exposes the ability
+            // to disable the behavior of activating entities on creation.  During conversion, the creation flow will be triggered,
+            // but entity activation requires a significant amount of subsystem initialization that's unneeded for conversion.
+            // So, to get around this, we swap out EditorEntityContextComponent with SliceConverterEditorEntityContextComponent.
+            components.erase(
+                AZStd::remove(
+                    components.begin(), components.end(), azrtti_typeid<AzToolsFramework::EditorEntityContextComponent>()),
+                components.end());
+            components.emplace_back(azrtti_typeid<AzToolsFramework::SliceConverterEditorEntityContextComponent>());
             return components;
         }
     } // namespace SerializeContextTools