Extend Arlington model for ETSI PAdES for DSS, VSS, and TSS

[petervwyatt]

Add extensions for ETSI PAdES for DSS, VSS, and TSS in PDF 1.7 as per PDF Errata #448.

Will add a new extension: fn:Extension(ETSI_EN_319_142_1, ...) as per both:

• ETSI EN 319 142-1 V1.1.1 (2016-04) as per ISO 32000-2:2020 spec: https://www.etsi.org/deliver/etsi_en/319100_319199/31914201/01.01.01_60/en_31914201v010101p.pdf

• ETSI EN 319 142-1 v1.2.1 (updated!): https://www.etsi.org/deliver/etsi_en/319100_319199/31914201/01.02.01_60/en_31914201v010201p.pdf - published but NOT officially supported by PDF 2.0 because ISO 32000-2:2020 uses a dated revision to

Note this may also include expanding on the Extensions.tsv dictionary, although the Adobe Extension Level 8 documentation mentioned as an alternative in the ETSI specs was never made public.

Arlington is NOT supposed to validate signatures, only ensure syntax and file validity so some details will not be encoded into the model.

The ESIC prefix used by ETSI PAdES is also not listed in the public list of registered 2nd class name prefixes at https://github.com/adobe/pdf-names-list. The Arlington extension will use the full ETSI document number for the extension identifier so if other ETSI extensions are made or exist they can be treated as a separate Arlington model extension. It also provides an implicit link to the ETSI specs if someone was to Google it!

[petervwyatt]

ESIC is now added to the official PDF names prefix registry in Github.

[petervwyatt]

Went with ETSI_PAdES as name of extension as it is shorter and easier to remember.