DATABASE_MEMORY calculation

DATABASE_MEMORY can raise to a maximum equivalent to the following calculation::

buffer pools + database heap (DBHEAP) + utility heap (UTIL_HEAP_SZ) + lock
list heap (LOCKLIST) + 2 * package cache (PCKCACHE_SZ) + catalog cache
(CATALOGCACHE_SZ) + shared sort heap threshold (SHEAPTHRES_SHR) if
INTRA_PARALLEL is ON + approximate 20% overhead