Overrides the newline definition for `\R` set when creating a new [type@GLib.
Regex]; any Unicode newline characters or character sequences are recognized as a newline by `\R`. These are `\r`, `\n` and `\r\n`, and the single characters U+000B LINE TABULATION, U+000C FORM FEED (FF), U+0085 NEXT LINE (NEL), U+2028 LINE SEPARATOR and U+2029 PARAGRAPH SEPARATOR. Since: 2.34