PO: Remove ini_set auto_detect_line_endings

[akirk]

In PHP 8.1, the admin_header will gets the php-error CSS class added for the suppressed notice for @ini_set( 'auto_detect_line_endings', 1 );

This adds code so that we can do without the ini setting and still handle old-style \r line-terminated files. This also adds a unit test for this.

Trac tickets:
https://core.trac.wordpress.org/ticket/64928
https://core.trac.wordpress.org/ticket/51383

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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Props akirk, westonruter, apermo.

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[github-actions]

Hi @akirk! 👋

Thank you for your contribution to WordPress! 💖

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[github-actions]

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[apermo]

LGTM, ran the patch locally and can confirm it works.

[apermo]

@akirk I created a new trac ticket specifically for this issue as I ran into that topic myself. Could you update the PR description to point at it.
https://core.trac.wordpress.org/ticket/64928

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 62093
GitHub commit: e40e13b

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.