Fix FlValue functions not marked for export (#18641)

shell/platform/linux/fl_value.cc

@@ -681,13 +681,14 @@ G_MODULE_EXPORT FlValue* fl_value_lookup(FlValue* self, FlValue* key) {
   return fl_value_get_map_value(self, index);
 }
 
-FlValue* fl_value_lookup_string(FlValue* self, const gchar* key) {
+G_MODULE_EXPORT FlValue* fl_value_lookup_string(FlValue* self,
+                                                const gchar* key) {
   g_return_val_if_fail(self != nullptr, nullptr);
   g_autoptr(FlValue) string_key = fl_value_new_string(key);
   return fl_value_lookup(self, string_key);
 }
 
-gchar* fl_value_to_string(FlValue* value) {
+G_MODULE_EXPORT gchar* fl_value_to_string(FlValue* value) {
   GString* buffer = g_string_new("");
   value_to_string(value, buffer);
   return g_string_free(buffer, FALSE);