Fix caustic bees getting bands of flying skulls (#9116)
Refactor sword brand probabilities
Use is_stackable_item to check displaying quantity in tiles (alefury).

Both removes a bit of code duplication and lets phantom mirrors show
that they can stack properly.
Add phantom mirrors to the \ screen.
Buff the rod of shadows.

Add 5 to the level of the selection (like Yred zombies); when the
absdepth of this crosses over into Depths it can start picking Depths
monsters as well.
Fix monsters casting freeze at other monsters.

It used the attacker's cold resistance instead of the defender's.
Fix monster tallying for objstat
Show iteration progress for objstat and mapstat
Tweak very ugly thing bands and Vaults placement

Previously ugly thing bands had a chance of getting very ugly things
in their band based on depth, and very ugly things used the same band
definition. This commit moves very ugly thing bands to their own data
and uses that old behavior. The ordinary ugly thing band now no longer
sometimes gets very ugly things, since the latter is far stronger than
the band leader.

I also tweak the placement of very ugly things in Vaults. They show up
similarly to how they did before on V:1-4, but don't nearly vanish on
V:5. The player now sees two very ugly things on average on V:5.
Reduce the numbers of derived undead in late D

Zombies and skeletons were rarely relevant post-Lair anyway.