- Replace SPACE_TYPE_LAST with SPACE_TYPE_NUM (adding 1).
- Rename RGN_TYPE_LEN to RGN_TYPE_NUM
This makes it possible to tag space-type/region-type combinations
with `bool tag[SPACE_TYPE_NUM][RGN_TYPE_NUM]` which reads more clearly
than `bool tag[SPACE_TYPE_LAST + 1][RGN_TYPE_LEN]`.