don't eagerly read file contents

[crockeo]

Motivation

Many usages of iter_files don't explicitly include skip_content, but they don't actually care about the contents of the files. This can slow down codegen when running against a large repository with many large files.

Content

This PR just adds skip_content to all of the iter_files references I could find which don't care about the file content.

Note that this...actually is all of the references. The more "right" way to do this may be to change iter_files to never return the contents of files, but I didn't want to make that kind of change w/o talking to the maintainers first.

Testing

Best-effort testing locally. Would like to chat w/ y'all to figure out how to effectively test a change like this.

Please check the following before marking your PR as ready for review

• I have added tests for my changes
• I have updated the documentation or added new documentation as needed

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[EdwardJXLi]

Hey there! Overall LGTM. Do you mind merging in from latest develop again? There's a couple changes that would fix the failing tests.

After that and the CLA check, I can then approve the pr 👍