[ruby/csv] CSV(): Add support for Ruby 3 (https://github.com/ruby/csv/pull/215)

The implementation of the `CSV` shortcut method is broken in Ruby 3
for calls that look like this:

```ruby
CSV(write_stream, col_sep: "|", headers: headers, write_headers: true) do |csv|
  ...
end
```

The above will result in the following error when the `CSV` method attempts to pass
on arguments to `CSV#instance`:

```
ArgumentError: wrong number of arguments (given 2, expected 0..1)
```

The issue is due to the changes in Ruby 3 relating to positional & keyword arguments.

This commit updates the `CSV()` shortcut implementation to work with Ruby 3, and also
updates the documentation for the shortcut method.

https://github.com/ruby/csv/commit/310dee45fa

lib/csv.rb

@@ -2650,8 +2650,13 @@ end
 #     c.read.any? { |a| a.include?("zombies") }
 #   } #=> false
 #
-def CSV(*args, &block)
+# CSV options may also be given.
-  CSV.instance(*args, &block)
+#
+#   io = StringIO.new
+#   CSV(io, col_sep: ";") { |csv| csv << ["a", "b", "c"] }
+#
+def CSV(*args, **options, &block)
+  CSV.instance(*args, **options, &block)
 end
 
 require_relative "csv/version"

test/csv/interface/test_read_write.rb

@@ -112,4 +112,13 @@ a;b;c
     assert_equal(CSV.instance,
                  CSV {|csv| csv})
   end
+
+  def test_instance_shortcut_with_io
+    io = StringIO.new
+    from_instance = CSV.instance(io, col_sep: ";") { |csv| csv << ["a", "b", "c"] }
+    from_shortcut = CSV(io, col_sep: ";") { |csv| csv << ["e", "f", "g"] }
+
+    assert_equal(from_instance, from_shortcut)
+    assert_equal(from_instance.string, "a;b;c\ne;f;g\n")
+  end
 end