Fix #70091: Phar does not mark UTF-8 filenames in ZIP archives

The default encoding of filenames in a ZIP archive is IBM Code Page
437. Phar, however, only supports UTF-8 filenames. Th

Fix #70091: Phar does not mark UTF-8 filenames in ZIP archives

The default encoding of filenames in a ZIP archive is IBM Code Page
437. Phar, however, only supports UTF-8 filenames. Therefore we have
to mark filenames as being stored in UTF-8 by setting the general
purpose bit 11 (the language encoding flag).

The effect of not setting this bit for non ASCII filenames can be seen
in popular tools like 7-Zip and UnZip, but not when extracting the
archives via ext/phar (which is agnostic to the filename encoding), or
via ext/zip (which guesses the encoding). Thus we add a somewhat
brittle low-level test case.

Closes GH-6630.

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