fix: preserve the type when indexed by an empty array

[TaiSakuma]

This PR is for part of #2377.
It fixes the problem where indexing with an empty array changes the type.
The PR includes associated tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.68%. Comparing base (b749e49) to head (fad6052).
⚠️ Report is 444 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/contents/content.py	77.12% <100.00%> (+2.30%)	⬆️

... and 196 files with indirect coverage changes

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[github-actions]

The documentation preview is ready to be viewed at http://preview.awkward-array.org.s3-website.us-east-1.amazonaws.com/PR3678

[ianna]

@all-contributors please add @TaiSakuma for code

[allcontributors]

@ianna

I've put up a pull request to add @TaiSakuma! 🎉

[ianna]

@TaiSakuma - This looks great! Thank you. The tests pass - it's good to be merged. Please, go ahead and merge it if you are done with it. I will leave it up to you if you would like to tackle the ak.flatten issue as a separate PR. Thanks!

[TaiSakuma]

@ianna, thanks. I'll look into the ak.flatten issue.