Implement codegen for rs backend

[almarklein]

• Write rs_mappings.py with enum->int mappings.
• Validate structs created in the code, and remove checking structs at runtime.
• Compare flags and report differences.
• Validate use of functions.
• Test some of the new code.
• Add tests that use the new codegen to verify that the code is up to date in CI.
• Better structure all codegen functions and make their use more similar.
• Since we now have more codegen-time validation, we can remove some runtime checks.
• Remove old codegen file that was still kept as a reference.

[almarklein]

Ready!