typings regression on TextOverflow children/label props

[giogonzo]

regression introduced in #1374
See discussion at: #1374 (comment)

Actually, re-looking at the source code of the component, label is always used. Since overflowing an empty string makes no sense, I'd make it required at least.
children is instead optional since it doesn't replace the label per se, but lets you customise rendering downstream after the ellipsis style has been applied by wrapping the label content in a span.

Current status is that it is impossible to use it correctly from a TS project if you want to customise children.