Rename text preprocess, direct item set methods

[KamikotoTkach]

Pull Request Description

I’ve added the following methods:

interface AnvilContainerWrapper {
    default void setRenameVisitor(Function<String, ItemStack> renameVisitor) {}
    default void setLeftItem(ItemStack item) {}
    default void setMiddleItem(ItemStack item) {}
    default void setRightItem(ItemStack item) {}
}

Changes Overview

• renameVisitor — a preprocessor for user input text. This allows formatting or transforming the text before it is directly applied to the item name.
• set*Item methods — allow setting items directly into specific slots. This enables logic such as:
  “If the player enters 0 — replace item X with a red block displaying an error message.”

Implementation Notes

• Implemented for Minecraft 1.16.5 as a reference example.
• Tested on a production server I maintain.
• No issues have been observed over the past 6 months.