Fixed misc slice conversion bugs

* Fixed crash caused by nesting the same slice twice
If the same slice is nested at multiple levels in the same slice hierarchy, the second conversion would reregister the prefab and crash.  Now that case is detected and the slice isn't reconverted.

* Fixed json array patches where multiple elements are removed.
The patches now generate removals from back to front, instead of front to back, so that the indices remain valid as each patch is applied.

Code/Framework/AzCore/AzCore/Serialization/Json/JsonMerger.cpp

@@ -607,10 +607,12 @@ namespace AZ
             }
             else if (source.Size() > target.Size())
             {
-                rapidjson::SizeType sourceCount = source.Size();
-                for (rapidjson::SizeType i = count; i < sourceCount; ++i)
+                // Loop backwards through the removals so that each removal has a valid index when processing in order.
+                for (rapidjson::SizeType i = source.Size(); i > count; --i)
                 {
-                    ScopedStackedString entryName(element, i);
+                    // (We use "i - 1" here instead of in the loop to ensure we don't wrap around our unsigned numbers in the case
+                    // where count is 0.)
+                    ScopedStackedString entryName(element, i - 1);
                     patch.PushBack(CreatePatchInternal_Remove(allocator, element), allocator);
                     resultCode.Combine(settings.m_reporting("Removed member from array in JSON Patch.",
                         ResultCode(Tasks::CreatePatch, Outcomes::Success), element));

Code/Framework/AzCore/Tests/Serialization/Json/TestCases_Patching.cpp

@@ -303,6 +303,29 @@ namespace JsonSerializationTests
             R"( { "foo": [ "bar", "baz" ] })");
     }
 
+    TEST_F(JsonPatchingSerializationTests, ApplyPatch_UseJsonPatchRemoveArrayMembersInCorrectOrder_ReportsSuccess)
+    {
+        CheckApplyPatch(
+            R"( { "foo": [ "bar", "qux", "baz" ] })",
+            R"( [
+                    { "op": "remove", "path": "/foo/2" },
+                    { "op": "remove", "path": "/foo/1" }
+                ])",
+            R"( { "foo": [ "bar" ] })");
+    }
+
+    TEST_F(JsonPatchingSerializationTests, ApplyPatch_UseJsonPatchRemoveArrayMembersInWrongOrder_ReportsError)
+    {
+        using namespace AZ::JsonSerializationResult;
+        CheckApplyPatchOutcome(
+            R"( { "foo": [ "bar", "qux", "baz" ] })",
+            R"( [
+                    { "op": "remove", "path": "/foo/1" },
+                    { "op": "remove", "path": "/foo/2" }
+                ])",
+            Outcomes::Invalid, Processing::Halted);
+    }
+
     TEST_F(JsonPatchingSerializationTests, ApplyPatch_UseJsonPatchRemoveOperationInvalidParent_ReportError)
     {
         using namespace AZ::JsonSerializationResult;
@@ -949,6 +972,27 @@ namespace JsonSerializationTests
         );
     }
 
+    TEST_F(JsonPatchingSerializationTests, CreatePatch_UseJsonPatchRemoveLastArrayEntries_MultipleOperationsInCorrectOrder)
+    {
+        CheckCreatePatch(
+            R"( [ "foo", "hello", "bar" ])", R"( [ "foo" ])",
+            R"( [
+                    { "op": "remove", "path": "/2" },
+                    { "op": "remove", "path": "/1" }
+                ])");
+    }
+
+    TEST_F(JsonPatchingSerializationTests, CreatePatch_UseJsonPatchRemoveAllArrayEntries_MultipleOperationsInCorrectOrder)
+    {
+        CheckCreatePatch(
+            R"( [ "foo", "hello", "bar" ])", R"( [])",
+            R"( [
+                    { "op": "remove", "path": "/2" },
+                    { "op": "remove", "path": "/1" },
+                    { "op": "remove", "path": "/0" }
+                ])");
+    }
+
     TEST_F(JsonPatchingSerializationTests, CreatePatch_UseJsonPatchRemoveObjectFromArrayInMiddle_OperationToUpdateMember)
     {
         CheckCreatePatch(