Remove OMR_GC_LEAF_BITS

[youngar]

We are thinking about getting rid of OMR_GC_LEAF_BITS as an optional feature, and making it permanent. This would remove some duplicated code in our object scanners which is never exercised.

To support people who don't use leaf maps, we could add default implementation of ObjectScanner::getNextSlotMap(uintptr_t *slotMap, uintptr_t *leafMap, bool *hasNextSlotMap) that defaults to setting the leaf map to 0. This would mean that the API stays the same. It might have some effect on performance for those who don't use leaf maps. I'm thinking something like:

virtual fomrobject_t *
getNextSlotMap(uintptr_t *slotMap, bool *hasNextSlotMap)
{
	Assert_MM_unimplemented();
}
virtual fomrobject_t *
getNextSlotMap(uintptr_t *slotMap, uintptr_t *leafMap, bool *hasNextSlotMap)
{
	*leafMap = 0;
	return getNextSlotMap(slotMap, hasNextSlotMap);
}

The alternatives are we leave it as an optional feature, or we force users to always specify *leafMap = 0 when they don't support leaf maps (edited)