This detects AESV3, and copies over the spec comments explaining what
needs to be done, but doesn't actually do it yet.
AESV3 is technically PDF 2.0-only, but
https://cipa.jp/std/documents/download_e.html?CIPA_DC-007-2021_E has a
1.7 PDF that uses it.
Previously we'd claim that we need a password to decrypt it.
Now, we cleanly crash with a TODO() \o/
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
Security handlers manage encryption and decription of PDF files. The
standard security handler uses RC4/MD5 to perform its crypto (AES as
well, but that is not yet implemented).
