Expose potion mixing API

[Vrganj]

Adds mixPotion and canMixPotion methods to simulate what a brewing stand would do.
I think it's a fair change since there's really not much potion API currently.

[lynxplay]

Generally a fan of the concept!
Some minor formatting and logic issues.

[Lulu13022002]

Seems you got tricked by parchment wrong param names for hasMix (mix doesn't do better really), potion is the ingredient and ingredient is the potion.

[Vrganj]

Looks like you're right. I kind of assumed potionItem referred to the same thing in either method. Thanks

[notTamion]

I don't really like how mixPotion returns the original itemstack when there is no mix available. I think we should either make this very clear in the jdocs or imo even better return null if the nms method returns the original itemstack

[Vrganj]

I don't really like how mixPotion returns the original itemstack when there is no mix available. I think we should either make this very clear in the jdocs or imo even better return null if the nms method returns the original itemstack

What if someone adds a noop potion mix? There's no way to differentiate between the two without also checking if the potion mix exists in the first place

[notTamion]

What if someone adds a noop potion mix? There's no way to differentiate between the two

it will still return a copy of the result, not the exact original so a simple reference check should do (at least if i remember correctly from earlier, on my phone rn so can't double check)