RLS: Add [ClientVisibilityFilter] attribute to C# module bindings

[joshua-spacetime]

Analogous to #[client_visibility_filter] and Filter::Sql in the rust module bindings.

/// A user only has access to their row
#[spacetimedb::client_visibility_filter]
const USER_FILTER: Filter = Filter::Sql("
    SELECT * FROM user WHERE identity = @sender
");