Closes#2588
SQLite internally implements `.clone` by doing something like piping
`.dump` into a new connection to a database attached to the file you
want. This PR implements that by adding an `ApplyWriter` that implements
`std::fmt::Write`, and refactors our current `.dump` plumbing to work
with any `Write` interface, so we can `.dump` to stdout or `.dump` to a
new connection, therefore cloning the database.
Reviewed-by: Nikita Sivukhin (@sivukhin)
Closes#2590
e4f424f9e6