The classes which currently implement the construction and parsing logic for the insert/update/delete commands are very poorly structured, inefficient and difficult to extend. Since as part of the 'Retryable Writes' project we will need to extend the set of parameters they support, this might be a good time to implement them in IDL.

Part of the work on this ticket should include a design of what the IDL parser should look like.

Note that this task is not strictly necessary for 'Retryable Writes', but it would make the write commands more extensible.