start of implementation of serializer keyword
(cherry picked from commit 74603ea0c780105a1e26d9281d643f8e0aa50e1b)
template for serializer
(cherry picked from commit 66b0ec120b6fcd0915c4e31bd64892e4fc7af548)
Support for serializer syntax in WebIDL
(cherry picked from commit f2510a9fc921cd00888523935f0a1b3c3ee79d89)