Create enum for item AH categories

[DioCar84]

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What does this pull request do?

Creates an enum xi.itemAHCategory that can be used when comparing the result of calling itemObj:getAHCat(). Replaced integer values with enum entry where getAHCat() is called.

Steps to test these changes

Several calls to itemObj:getAHCat() with different items to ensure the correct Boolean value is returned when comparing the various categories.

[github-actions]

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[zach2good]

While you're doing this, you should probably also use the enum in the few places where that function is called:

[DioCar84]

Yes excellent suggestion @zach2good. Brain fart moment... I have amended the PR to include using the enum.