📝 Inappropriate usages of `function` word in API reference

[LVMVRQUXL]

📝 Description

Due to inappropriate usages of the function word in the API reference, we want to use the function or the method wording following these definitions:

• A function is a piece of code that is callable from its name (like println).
• A method is a piece of code that is attached to an object and is callable from its name (like Any.toString).

✅ Checklist

• [x] 🐛 Replace function by method in the documentation of method declarations.
• [x] 📝 Update the unreleased changelog for this issue.