General PDF object model improvements

[petervwyatt]

• Add a cross-reference to ISO 32000-2:2020 in each TSV file, such as against the Type or Subtype key in the right-most "Note" field. Could be a Table number, clause number or a GitHub URL to a specific Errata at https://github.com/pdf-association/pdf-issues/issues

• Ensure all integers are checked for an identified range of valid values - in particular whether zero is sensible

• Ensure all numberss are checked for an identified range of valid values - in particular whether zero is sensible

• Ensure all arrays are checked for minimum and maximum number of elements - in particular, whether an empty array is sensible

• Check each rectangle to see if a degenerate rectangle (zero height OR zero width OR both) makes sense

• Support merged widgets and fields as allowed under clause 12.5.6.19 - is the best way to add field keys to all widget TSVs??

• go back through all the old Adobe PDF references and add/update as necessary, especially for things that were removed

[petervwyatt]

Further idea for cross-referencing to ISO 32000-2:2020 - is there sufficient information to construct a fragment identifier?

[petervwyatt]

• Also check the usage of _UniversalArray and _UniversalDictionary to confirm that additional specialized objects with additional semantics would not be more appropriate