Add zip files with password encryption

[jeffhandley]

In preparation for a PR that implements dotnet/runtime#68897, adding an ZipArchiveEntry.IsEncrypted property, this PR adds 3 zip files for testing.

• encrypted_entries_weak.zip includes 2 entries with "weak" (ZipCrypto) encryption and 2 entries that are unencrypted
• encrypted_entries_aes256.zip includes 2 entries with "strong" (AES-256) encryption and 2 entries that are unencrypted
• encrypted_entries_mixed.zip includes 1 entry with "weak", 1 entry with "strong", and 2 entries with no encryption

For each encrypted entry, there is a comment on the entry indicating what the password for that entry is. Each file contains a small amount of content, with simply FileName: <filename-without-ext>.

[jozkee]

1. I see the entries are blank, which is OK for ZipArchiveEntry.IsEncrypted, but if the files were not empty, we could re-use the assets for the tests of the rest of the Zip entryption APIs (check the contents are correctly preserved/not garbled).
2. encrypted_entries_mixed.zip doesn't have the password in the Comment.
   

[jeffhandley]

@jozkee Thanks for the feedback on this. I updated the zips to:

1. Put contents into each file (simply Filename: <filename-without-extension>)
2. Rename the "strong" file to "aes256" in case we want to extend the coverage later
3. Ensure all encrypted files have comments with their passwords (and changed the "mixed" passwords to be different between encrypted entries)

[jeffhandley]

Here's the branch where the feature is implemented and the tests can be seen:
https://github.com/dotnet/runtime/compare/main...jeffhandley:jeffhandley/zippassword?expand=1

[jozkee]

Thanks!