scanner: Use the new atomic marshal/destroy function

Use the new flagged marshal+destroy function in generated code.

It's intended as a replacement for all existing wl_proxy_marshal_*
functions, so I've used it to replace them all. This results in a large
update to the scanner test files as well.

We now pass the new WL_MARSHAL_FLAG_DESTROY flag when appropriate, so
the race condition in #86 caused by releasing the display mutex between
marshalling the proxy and destroying the proxy is now gone.

Fixes #86

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>