HPCC-12561 Implement 1st set of xml read improvements

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-12561 Also speed up boolean xml reading

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6628 from ghalliday/issue12561

HPCC-12561 Implement 1st set of xml read improvements

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>