Add support for writing binary to file system

[inokawa]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

https://github.com/orgs/remarkjs/discussions/1473

This PR removes the stringification of Uint8Array before writing to the file system, that allows us outputting binary data from compiler (e.g. .docx, images) with cli like remark-cli.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (6f35eae) to head (82f06c9).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #86   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           23        23           
  Lines         3214      3214           
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  Hits          3214      3214           

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[wooorm]

Wrapper function seems unneeded, can just copy/paste the value twice?
Or, stash the return value directly in the variable?
Also, more vaguely, what’s a good test for binary? What did you pick? Were there alternatives you considered?

[inokawa]

The problem was non-UTF-8 string data was transformed to UTF-8 string data by TextDecoder before saving. I've added a new test with an Uint8Array including UTF-8 string for clarification (it will succeed with/without the fix).

I'm not an expert on handling binary in JS, but I think we can say the data is the same if the values at every indexes in a TypedArray like Uint8Array is the same. I used deepStrictEqual for that. I'm not sure we need to check data wrapped with other TypedArrays like Float16Array also.