[3.14] GH-139951: Fix major GC performance regression. Backport of GH-140262 (GH...

[3.14] GH-139951: Fix major GC performance regression. Backport of GH-140262 (GH-140447)

* Count number of actually tracked objects, instead of trackable objects. This ensures that untracking tuples has the desired effect of reducing GC overhead
* Do not track most untrackable tuples during creation. This prevents large numbers of small tuples causing execessive GCs.