[3.0.0 prep] New pcap_* bindings

[cicku]

• pcap_init
• pcap_dump_ftell
• pcap_dump_ftell64
• pcap_dump_file
• pcap_snapshot

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pcap_init fixes #383 and supersedes #384.

Must be merged after #400, and a rebase will be done then.

[cicku]

Ready:

Reason of additions:

• pcap_init: Non-ASCII handling
• pcap_dump_ftell64/ftell: Size-based file rotation needs
• pcap_snapshot: For Capture<Offline> the snapshot length comes from the file header and is otherwise unknowable

I'm open to drop pcap_dump_file if you feel like certain low level functions are not needed. Instead one can always flush() and offset().

[Wojtek242]

Looks good. One minor comment to update a comment.

[Wojtek242]

I am not familiar with the term "unpaired surrogate". Is this a standard term in Windows or your term? If it's standard in Windows it can stay. If not, can you rephrase to rephrase this to make it a bit clearer?

[cicku]

This is Unicode stuff. From U+D800 to U+DFFF are called (1x low + 1x high) surrogates and used for UTF-16. High and low surrogates must be in a pair to present anything higher than 2^16.

https://learn.microsoft.com/en-us/windows/win32/intl/surrogates-and-supplementary-characters

https://www.rfc-editor.org/info/rfc2781/