Add changers to ExprBookPages

[UnderscoreTud]

Description

This PR adds changers to the book pages expression

---

Target Minecraft Versions: Any Requirements: None Related Issues: I don't believe there are any

[TheLimeGlass]

This class has been marked to be recoded at some point, so if you're adding changers to this class, the team is most likely going to suggest other additions to this class. First off it can be a PropertyExpression. Yes it's possible with the existing syntaxes to still have support for property expression.

[UnderscoreTud]

Should I do it in this PR?