Fix Scorching Ray exposure not applying when using calculate maximum sustainable stages option

[Paliak]

Fixes #5162 .

Description of the problem being solved:

Scorching ray applies exposure when at maximum stages. 222a1c5 moved the logic that calculates maximum sustainable stages for a few skills to after buffs/debuffs are applied to take arcane surge cast speed buff into consideration causing mods that use stage count as thresholds to not be added when they should.

mod("FireExposure", "BASE", nil, 0, 0, { type = "GlobalEffect", effectType = "Debuff", effectName = "Fire Exposure", effectCond = "ScorchingRayMaxStages" }),

Before screenshot:

After screenshot:

[Wires77]

Is there a reason we didn't reuse the buff calculation logic from ~line 1818 for this? Seems like we could've popped that into a function and recalculated for those certain skills.

Edit: Discussion in Discord answered this:

[7:59 AM]Paliak: Couldn't think of a better way without rewriting a good chunk of CalcPerform.
[7:59 AM]Paliak: lots of mods get processed sequentially and that sometimes breaks things.
[7:59 AM]Paliak: kinda like with the gems thing that i made a pr for some time ago.
[7:59 AM]Paliak: where due to the order of processing them a flag was not being applied
[8:00 AM]QuickStick123: Why do you need to merge the buff into those list as well? 
[8:00 AM]QuickStick123: Or is it just newly added ones.
[8:00 AM]Paliak: it's just new ones
[8:00 AM]Paliak: it's in case something needs them
[8:01 AM]QuickStick123: Fair enough it seems to work.
[8:01 AM]Paliak: Yeah i know it's ugly but we'd need some sort of callback based system for processing this kind of stuff to make it nicer.