arrow

GH-34119: [C#] Add [] operator to Schema (#34126)

Add the `[]` operator to Schema that retrieves a field by index if an int is passed, or retrieved a field by name if a string is passed.
* Closes: #34119

Lead-authored-by: DanTm99 <danyaal99@hotmail.co.uk>
Co-authored-by: Danyaal Khan <danyaal99@hotmail.co.uk>
Signed-off-by: Weston Pace <weston.pace@gmail.com>