Avoid PDF/A-3 test failure

[abelykh0]

Avoid PDF/A-3 test failure (ISO 32000-1:2008, 9.7.4, Table 117 requires that all embedded Type 2 CIDFonts in the CIDFont dictionary shall contain a CIDToGIDMap entry that shall be a stream mapping from CIDs to glyph indices or the name Identity, as described in ISO 32000-1:2008, 9.7.4, Table 117)

There's no easy way to do it otherwise. This is what works, but it is really ugly

			// HACK: Add required /CIDToGIDMap /Identity to fonts
			//var fontTable = document.FontTable;
			//var documentFonts = fontTable._fonts;
			var fontTableProperty = typeof(PdfDocument).GetProperty("FontTable", BindingFlags.NonPublic | BindingFlags.Instance);
			object fontTable = fontTableProperty.GetValue(document, null);
			var fontsField = fontTable.GetType().GetField("_fonts", BindingFlags.NonPublic | BindingFlags.Instance);
			var documentFonts = (IDictionary<string, PdfFont>)fontsField.GetValue(fontTable);
			foreach (var documentFont in documentFonts.Values)
			{
				if (documentFont.Elements.TryGetValue("/DescendantFonts", out PdfItem descendantFontItem))
				{
					PdfArray descendantFont = (PdfArray)descendantFontItem;
					var descendantFontDictionary = (PdfDictionary)((PdfReference)descendantFont.Elements[0]).Value;
					descendantFontDictionary.Elements.SetName("/CIDToGIDMap", "/Identity");
				}
			}