HPCC-12351 Use an internal buffer for small dyanamic strings

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-12351 Switch various StringBuffers to StringAttrs

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-12351 Updates following review

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6635 from ghalliday/issue12351

HPCC-12351 Use an internal buffer for small dynamic strings

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>