HPCC-12452 Allow configurable bucket sizes for the heap allocator

* Using a lookup table generates more efficient code, and is more flexible

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6578 from ghalliday/issue12452

HPCC-12452 Allow configurable bucket sizes for the heap allocator

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Mark Kelly <mark.kelly@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>