Create ReplDumpTask/ReplDumpWork for dumping out metadata

– The current bootstrap code generates dump metadata during semantic analysis which breaks security and task/work abstraction. It also uses existing classes (from Export/Import world) for code reuse purpose, but as a result ends up dealing with a lot if-then-elses. It makes sense to have a cleaner abstraction which uses ReplDumpTask and ReplDumpWork (to configure the Task). Also perhaps worth evaluating ReplLoadTask/ReplLoadWork for load side.

– Also consider including here: avoid deserializing notification and serializing again during repl dump. The notification should contain all info already (if not, fix it)