extensions: printing: extract and use margins in printing backend 2/*

Extract margins from the print ticket and pass them to a printer via
CUPS.

The feature is controlled by the kApiPrintingMarginsAndScale feature
flag. When enabled, extensions can specify margins via the
printer.margins ticket item in the Cloud Job Ticket format.

Design doc:
https://docs.google.com/document/d/1EgbaHpFDl8sEMYDaeL0oAta3lSa_x4Nv9KmSfScyKRk

Bug: 316999874, 308709702
Change-Id: I70db75d70aff0169f5e51b639b64e00f68a5ea9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6357051
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Nathan Muggli <nmuggli@google.com>
Reviewed-by: Alan Screen <awscreen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1442598}