Revert the use of different exception, because this way the request body does not get added to the error response meta

Author: Bart Koelman

src/JsonApiDotNetCore/Errors/ForbiddenClientGeneratedIdException.cs

@@ -182,7 +182,7 @@ private static void AssertHasNoId(IResourceIdentity identity, RequestAdapterStat
             if (identity.Id != null)
             {
                 using IDisposable _ = state.Position.PushElement("id");
-                throw new ForbiddenClientGeneratedIdException(state.Position.ToSourcePointer());
+                throw new ModelConversionException(state.Position, "The use of client-generated IDs is disabled.", null, HttpStatusCode.Forbidden);
             }
         }
 

src/JsonApiDotNetCore/Serialization/RequestAdapters/ResourceIdentityAdapter.cs

@@ -459,9 +459,11 @@ public async Task Cannot_create_resource_with_client_generated_ID()
 
             ErrorObject error = responseDocument.Errors[0];
             error.StatusCode.Should().Be(HttpStatusCode.Forbidden);
-            error.Title.Should().Be("The use of client-generated IDs is disabled.");
+            error.Title.Should().Be("Failed to deserialize request body: The use of client-generated IDs is disabled.");
             error.Detail.Should().BeNull();
             error.Source.Pointer.Should().Be("/atomic:operations[0]/data/id");
+
+            responseDocument.Meta["requestBody"].ToString().Should().NotBeNullOrEmpty();
         }
 
         [Fact]

test/JsonApiDotNetCoreTests/IntegrationTests/AtomicOperations/Creating/AtomicCreateResourceTests.cs

@@ -456,9 +456,11 @@ public async Task Cannot_create_resource_with_client_generated_ID()
 
             ErrorObject error = responseDocument.Errors[0];
             error.StatusCode.Should().Be(HttpStatusCode.Forbidden);
-            error.Title.Should().Be("The use of client-generated IDs is disabled.");
+            error.Title.Should().Be("Failed to deserialize request body: The use of client-generated IDs is disabled.");
             error.Detail.Should().BeNull();
             error.Source.Pointer.Should().Be("/data/id");
+
+            responseDocument.Meta["requestBody"].ToString().Should().NotBeNullOrEmpty();
         }
 
         [Fact]