Add change note

Author: owen-mc

go/ql/lib/change-notes/2024-05-23-models-as-data-argument-receiver.md

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+---
+category: feature
+---
+* When writing models-as-data models, the receiver is now referred to as `Argument[receiver]` rather than `Argument[-1]`.
+* Neutral models are now supported. They have no effect except that a manual neutral summary model will stop a generated summary model from having any effect.