HPCC-10294 Add comments to records and some functions in Std.File

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-10294 Fix comments following code review and other clean up.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5997 from ghalliday/issue10294

HPCC-10294 Add comments to records and some functions in Std.File

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>