[ty] Add a note to the diagnostic if a new builtin is used on an old Python version (#18068)

## Summary

If the user tries to use a new builtin on an old Python version, tell
them what Python version the builtin was added on, what our inferred
Python version is for their project, and what configuration settings
they can tweak to fix the error.

## Test Plan

Snapshots and screenshots:


![image](https://github.com/user-attachments/assets/767d570e-7af1-4e1f-98cf-50e4311db511)

crates/ty_python_semantic/resources/mdtest/diagnostics/unresolved_reference.md

@@ -0,0 +1,14 @@
+# Diagnostics for unresolved references
+
+## New builtin used on old Python version
+
+<!-- snapshot-diagnostics -->
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+aiter  # error: [unresolved-reference]
+```