HPCC-12028 Improve the code generated for ifblocks

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-12028 Cache the ifblock size in the deserialize code

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6317 from ghalliday/issue12028

HPCC-12028 Cache the ifblock size in the deserialize code

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>