A `count_rows` method that takes a filter was recently added to
`LanceTable`. This PR adds it everywhere else except `RemoteTable` (that
will come soon).
* Easy to type
* Handle `String, &str, [String] and [&str]` well without manual
conversion
* Fix function name to be verb
* Improve docstring of Rust.
* Promote `query` and `search()` to public `Table` trait