loot system fixes and tweaks

[qndel]

Part 2 of the "oneliners that flip the game upside down"
Now required because of #2763
Turns out the previous loot fix actually makes some uniques unfindable as they were only findable because of that bug which we fixed. This will apply to all uniques dropped in devilutionx and they might morph into a different unique of the same base in vanilla - In my opinion that's acceptable as there's literally no way we can keep it compatible so there's no reason to even attempt to.
I think that along with #2763 this puts Diablo's loot in a nice state and I'd even consider the game almost playable ;)

• Needs a fat changelog entry!

#edit
Added 1 way compatibility - uniques from vanilla won't morph, but devx uniques will morph in vanilla - there's simply no way around that :P

It's worth considering if we wouldn't want to improve the rng for regular magic items as well, since this PR is introducing a way to tell the difference between vanilla items and devilutionx ones.

[julealgon]

Scary. I like it.

[galaxyhaxz]

LGTM. I tested against the PR I made 2 years ago (#540) and they both generate the exact same results. I still prefer my cleanup however as it makes the logic a bit more understandable.

[qndel]

@AJenbo if this goes into 1.4.0, I believe #2763 should be reverted for 1.3.0. They really need to go together imo.

[AJenbo]

Could you do so and then add it to this PR?

[agris-codes]

This is going to be a rehash of my feedback contained in another issue, but I think this is the correct location for it.

In fixing this issue, I think the problem of best-of-class items being unable to drop in higher difficulties due to the current qlvl minimum defined as mlvl / 2 should be fixed as well. I propose that the qlvl floor be decreased to mlvl / 3, which means items such as Obsidian Tower Shield of the Ages (qlvl 25), Full Plate Mail of Sorcery (qlvl 25), and "Weapon of Haste" derivatives (qlvl 27) can all be found as drops in higher difficulties, while also extending the period over which the player can discover very good items but not best-of-class (Weapon of Speed, for example). Plus add in all the uniques at qlvl 15 to 25 that are filtered by the current qlvl floor (http://www.bigd-online.com/JG/Body/JG3-5.html). It lets the loot system's depth really shine outside of the vendor system.

It also resolves another peculiarity of the current system, wherein some base item types are are over-represented in drops on Nightmare / Hell due to how they satisfy min(qlvl) requirements.

I certainly do not understand the nuances of how base item is decided and then affixes applied as well as others, like @qndel, but my suggestion of decreasing the floor as described above would go a long way to incentivizing playing at higher difficulties, to hunt for rare items.

The more monster slaying and less vendor shopping, the better.

[obligaron]

Additional Question: if we change the item generation in a 1 way compatible way. Should we also use a better random number generator for the new item generator? It's not backwards compatible anyway.

[qndel]

Additional Question: if we change the item generation in a 1 way compatible way. Should we also use a better random number generator for the new item generator? It's not backwards compatible anyway.

Can't see why not