[red-knot] Auto generate statement nodes (#16645)

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## Summary

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Part of #15655 

Replaced statement nodes with autogenerated ones. Reused the stuff we
introduced in #16285. Nothing except for copying the nodes to new
format.

## Test Plan

Tests run without any changes. Also moved the test that checks size of
AST nodes to `generated.rs` since all of the structs that it tests are
now there.
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Author: Glyphack