Extend Arlington extension to document OpenOffice and LibreOffice custom trailer keys

[petervwyatt]

In file trailer and XRefStream:

• /AdditionalStreams [/application#2Fvnd#2Eoasis#2Eopendocument#2Etext 6 0 R] (ODT document) - an array of pairs of (MIME as a name + indirect references to streams)

• /DocChecksum /DocChecksum /C2ABA76E903B138C5EC5DE44D0AE2A77 (MD5 as a name)

See https://git.libreoffice.org/core/+/refs/heads/master/vcl/source/gdi/pdfwriter_impl.cxx

[petervwyatt]

According to https://bugs.documentfoundation.org/show_bug.cgi?id=66580, /DocChecksum and /AdditionalStreams were added to OpenOffice on 2007-03-26.

In the LibreOffice git repository this is commit d217c079d7b3ca7b5039428594e7cdfdf9a0c4a9

From quick code skim, looks like this might occur in any PDF from PDF 1.2 (historically)

[crlf0710]

Are these correct uses of first-class names?

[petervwyatt]

Nope. But its what they've been doin' since 2007-ish so there are plenty in the wild!
I have a few issues open with them ATM to fix conformance to PDF/A and PDF/UA subsets...