Pass the ignoreErrors API option to the FontFaceObject constructor, and utilize it in getPathGenerator to ignore missing glyphs

Obviously it's still not possible to render non-embedded fonts as paths, but in this way the rest of the page will at least be allowed to continue rendering.

*Please note:* Including the 14 standard fonts in PDF.js probably wouldn't be *that* difficult to implement. (I'm not a lawyer, but the fonts from PDFium could probably be used given their BSD license.)
However, the main blocker ought to be the total size of the necessary font data, since I cannot imagine people being OK with shipping ~5 MB of (additional) font data with Firefox. (Based on the reactions when the CMap files were added, and those are only ~1 MB in size.)

test/pdfs/issue4244.pdf.link

@@ -0,0 +1 @@
+https://web.archive.org/web/20180613082417/https://tcpdf.org/files/examples/example_026.pdf

test/test_manifest.json

@@ -2267,6 +2267,13 @@
       "rounds": 1,
       "type": "eq"
     },
+    {  "id": "issue4244",
+       "file": "pdfs/issue4244.pdf",
+       "md5": "26845274a32a537182ced1fd693a38b2",
+       "rounds": 1,
+       "link": true,
+       "type": "eq"
+    },
     {  "id": "preistabelle",
       "file": "pdfs/preistabelle.pdf",
       "md5": "d2f0b2086160d4f3d325c79a5dc1fb4d",