Skip and warn on emoji import when name conflicts with system emoji (#19516)

This changes import behavior related to emoji imports when the name
conflicts with the name of a system emoji. Previously, the import
would fail, but now a warning is logged and the conflicting emoji
is skipped.

app/import_validators.go

@@ -560,6 +560,8 @@ func validateDirectPostImportData(data *DirectPostImportData, maxPostSize int) *
 	return nil
 }
 
+// validateEmojiImportData validates emoji data and returns if the import name
+// conflicts with a system emoji.
 func validateEmojiImportData(data *EmojiImportData) *model.AppError {
 	if data == nil {
 		return model.NewAppError("BulkImport", "app.import.validate_emoji_import_data.empty.error", nil, "", http.StatusBadRequest)
@@ -569,14 +571,14 @@ func validateEmojiImportData(data *EmojiImportData) *model.AppError {
 		return model.NewAppError("BulkImport", "app.import.validate_emoji_import_data.name_missing.error", nil, "", http.StatusBadRequest)
 	}
 
-	if err := model.IsValidEmojiName(*data.Name); err != nil {
-		return err
-	}
-
 	if data.Image == nil || *data.Image == "" {
 		return model.NewAppError("BulkImport", "app.import.validate_emoji_import_data.image_missing.error", nil, "", http.StatusBadRequest)
 	}
 
+	if err := model.IsValidEmojiName(*data.Name); err != nil {
+		return err
+	}
+
 	return nil
 }