HPCC-9507 Add STD.STR.REPEAT(text, n)

Returns a string containing text repeated n times.

 * @param text          The string to be repeated.
 * @param n             Number of repetitions.
 * @return              A string containing n concatenations of the string text.

Signed-off-by: jamienoss <james.noss@lexisnexis.com>
Merge pull request #5171 from jamienoss/issue9507-add-std.str.repeat

HPCC-9507 Add STD.STR.REPEAT(text, n)

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>