Fix plural item aliases

[Abrightday166]

Problem

Item aliases for items ending in 's' are semantically wrong in the plural: e.g. "Cobblestone Stairss" and "Ancient Debriss"

Solution

For generated aliases, check that the item name doesn't end with an 's' before adding the '¦s' plural marker.

Testing Completed

Tested on paper-26.1.2-74 fresh server.
Manual testing via effect commands:

BEFORE
Executing 'send items of player's inventory'
64 oak stairss
64 spruce stairss
64 birch stairss
64 jungle stairss

AFTER
Executing 'send items in player's inventory'
64 oak stairs
64 spruce stairs
64 birch stairs
64 jungle stairs

and confirmed that other items are unaffected by the change.

Supporting Information

I would have just made an issue but I didn't want to waste your time so you get to waste your time reading this pr instead.

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Completes:

• Broadcasting item stacks with 2 or more items adds an s at the end (seems intentional but it does cause issues) #8311

Related: none
AI assistance: none

[APickledWalrus]

I would prefer to see a more robust solution that makes use of the plural utilities, such as

Skript/src/main/java/ch/njol/skript/util/Utils.java

Line 344 in 8265733

public static String toEnglishPlural(String word) {

I don't believe there is a direct method matching this use case, but you could add one.