Fix filename extension stripping bug and clean up dev tooling

[f2cmb]

Summary

The main fix: str_replace($ext, '', $file_name) stripped every occurrence of the extension string from the filename, not just the suffix. Example: css.style.css became style instead of css.style. Fixed with pathinfo() + substr().

Since I was in there anyway, I cleaned up a few things that were bugging me:

• PHPCompatibility testVersion was set to 5.6- but the plugin requires PHP 8.0+. Updated to 8.0-.
• Removed the convert*ToExceptions attributes from PHPUnit config (deprecated in 9.5, gone in 10).
• Fixed typos in comments ("chats" → "chars", "caracters" → "characters") and renamed test_convert_at_sign_to_dashes to test_remove_at_sign, since the @ is stripped, not converted to a dash.

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Note

High Risk
Changes core upload filename sanitization and updates the special-character lists; the latter introduces non-standard quote characters that could cause parsing/runtime issues if not intentional. Also updates PHP compatibility/testing configs, which may affect CI outcomes.

Overview
Fixes a filename extension handling bug in bea_sanitize_file_name() by switching from regex/str_replace() to pathinfo() + substr() so only the trailing extension is removed and then re-appended.

Updates the set of characters escaped by bea_sanitize_file_name_chars() and cleans up related comments, but also changes the quoting of these literals (now using typographic quotes), which may alter behavior or even break parsing if unintended.

Modernizes dev tooling by bumping PHPCompatibility to 8.0- in phpcs.xml, removing deprecated PHPUnit convert*ToExceptions flags, and renaming a unit test to reflect that @ is removed rather than converted.

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[herewithme]

Merci pour le report de bugs, j'ai repris la prop ici : #29