Fix MIME guessing of extension from type

[paulbalandan]

Description
Fixes #6046 by relying on the path extension as the $proposedExtension argument to Config\Mimes::guessExtensionFromType(). The extension is derived using pathinfo()

However, this fix also changes the behavior of the guessing if a proposed extension is given. Previously, if the proposal is invalid, the guessing ends and returns null. Now, this early termination is removed and the guessing is continued using the array mapping of extension to MIME types.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

Some edge cases I didn't see.

[paulbalandan]

According to https://cdn.jsdelivr.net/gh/jshttp/mime-db@v1.49.0/db.json and https://gitlab.freedesktop.org/xdg/shared-mime-info/-/raw/master/data/freedesktop.org.xml.in which are used by Symfony in updating their MIME types, the first one is the IANA recognized MIME type.

[samsonasik]

changelog and/or upgrading doc need update to copy app/Config/Mimes.php after update to 4.2?

[paulbalandan]

Rebased to add the relevant docs.

[lonnieezell]

I had to read through this a couple of times, but I believe the changes still keep the intended security features of those methods in place.

[kenjis]

@paulbalandan Thank you!