Allow keywords as identifiers

[parched]

This matches the behavior of flatc.

This feels a little hacky but this is my first time seeing larlpop so I'm unsure if there's a better way.
Guidance on suitable tests would be appreciated too.

The specific use case I have is fields called attribute.

Checklist

• Updated CHANGELOG.md with relevant changes
• Added tests for any new/fixed functionality
• Added/updated documentation for new/changed code
• Checked that README.md still makes sense (and updated it if necessary)

[TethysSvensson]

I don't know if there is a better way either but I think this approach is probably good enough.

You can add tests in the test/files/invalid and test/files/valid directories to test the core parsing.

However I think it also makes sense to test the code generation in this case. That would be in test/rust-test-2021/api_files.

I think using keywords as identifiers is a bit cursed, but I'm not inherently against it. I'll take a better look later.

[TethysSvensson]

By the way, is there anything preventing you from simply renaming the field to something that isn't a reserved keyword?

[parched]

By the way, is there anything preventing you from simply renaming the field to something that isn't a reserved keyword?

I would have to update the thousand-odd places we currently use it in our codebase -- it isn't a simple find-and-replace because the word is used in other contexts too.

[parched]

@TethysSvensson I've rebased and added the changelog entry, so this should be good to go if you're happy with it.