feat: Add PDF/A support and source attachment to PDF.

[kesara]

Fixes #1085

This change requires WeasyPrint >=61.0.

• Generate a valid PDF/A-3B document.
• Attach source XML to PDF file.

[kesara]

With updates from Kozea/WeasyPrint#1869 xml2rfc can generate a PDF file that confirms with PDF/A-3B standard.

Sample file: https://t4.fq.nz/rfc9527.pdf

VeraPDF output:

<?xml version="1.0" encoding="utf-8"?>
<report>
  <buildInformation>
    <releaseDetails id="core" version="1.24.1" buildDate="2023-06-22T10:38:00Z"></releaseDetails>
    <releaseDetails id="validation-model" version="1.24.1" buildDate="2023-06-22T11:37:00Z"></releaseDetails>
    <releaseDetails id="gui" version="1.24.1" buildDate="2023-06-22T14:19:00Z"></releaseDetails>
  </buildInformation>
  <jobs>
    <job>
      <item size="91087">
        <name>/docs/rfc9527.pdf</name>
      </item>
      <validationReport jobEndStatus="normal" profileName="PDF/A-3B validation profile" statement="PDF file is compliant with Validation Profile requirements." isCompliant="true">
        <details passedRules="144" failedRules="0" passedChecks="40904" failedChecks="0"></details>
      </validationReport>
      <duration start="1707442324695" finish="1707442325181">00:00:00.486</duration>
    </job>
  </jobs>
  <batchSummary totalJobs="1" failedToParse="0" encrypted="0" outOfMemory="0" veraExceptions="0">
    <validationReports compliant="1" nonCompliant="0" failedJobs="0">1</validationReports>
    <featureReports failedJobs="0">0</featureReports>
    <repairReports failedJobs="0">0</repairReports>
    <duration start="1707442324642" finish="1707442325193">00:00:00.551</duration>
  </batchSummary>
</report>

Poppler pdfdetach output:

pdfdetach -list rfc9527.pdf
1 embedded files
1: rfc9527.xml

[ajeanmahoney]

I looked at https://t4.fq.nz/rfc9527.pdf, and I can save and open the attached XML file.
Some observations:

• The WeasyPrint-generated PDF is smaller (89K) than the pdfaPilot PDF (202K).
• The Document Properties dialog box shows the following differences (if not listed here, then the properties match):
  • List of authors:
    • WeasyPrint-generated PDF: semicolon-delimited and not in quotes
    • pdfaPilot-generated PDF: comma-delimited and in double quotes
  • Keywords:
    • WeasyPrint-generated PDF: contains the abstract in double quotes
    • pdfaPilot-generated PDF: empty
  • Created and Modified:
    • WeasyPrint-generated PDF: empty
    • pdfaPilot-generated PDF: has timestamps

rfc9527_properties_screenshot.pdf
rfc9527_weasy_2_properties_screenshot.pdf