Isolate shrine/quest pool RNG from global RNG state

[StephenCWills]

This PR begins the process of isolating seeded random number generators from the global RNG state. I expect that item generation and dungeon generation will each need a fairly sizeable set of changes to ensure RNG instances are being passed around appropriately to avoid compatibility issues so I plan to do the same for each of them in separate PRs. After those are out of the way, we can look into potentially scrubbing out the remaining calls to SetRndSeed() and changing up how various seeds get generated.

[julealgon]

What's the overarching idea behind this? Do you want for each "area" of the game to have a different seed potentially?

[StephenCWills]

Eventually, I'd like to fix #6261. But also, refer to diasurgical/devilution#64 (comment) for a description of how abuse of the SetRndSeed() function can cause problems for the global RNG.

EDIT: You may also want to refer to a pair of PRs I submitted in the past which provide a more concrete example of an issue caused by this lack of RNG isolation: #3296 and #3314

[StephenCWills]

Rebased, on a whim.