Serializing and deserializing SharedArrayBuffer

Additionally, define StructuredSerializeForStorage when for
serializable objects need to be stored more persistently.

Tests: web-platform-tests/wpt#5003.

Fixes #2260 (by being the last in a set of fixes). Closes
tc39/proposal-ecmascript-sharedmem#144 and closes
tc39/proposal-ecmascript-sharedmem#65.

Author: domenic