Fix handling of symbolic fonts and unicode cmaps.

In issue 12120, the font has a 1,0 cmap and is marked symbolic which
according to the spec means we should directly use the cmap instead of
the extra steps that are defined in 9.6.6.4.

However, just fixing that caused bug 1057544 to break. The font in bug
1057544 has a 0,1 cmap (Unicode 1.1) which we were not using, but is
easy to support. We're also easily able to support some of the other
unicode cmaps, so I added those as well.

There was also a second issue with bug 1057544, the cmap doesn't have
a mapping for the "quoteright" glyph, but it is defined in the post
table. To handle this, I've moved post table as a  fallback for any
font that has an encoding.

test/pdfs/.gitignore

@@ -88,6 +88,7 @@
 !issue10665_reduced.pdf
 !issue11016_reduced.pdf
 !issue11045.pdf
+!bug1057544.pdf
 !issue11150_reduced.pdf
 !issue11242_reduced.pdf
 !issue11279.pdf
@@ -192,6 +193,7 @@
 !issue4260_reduced.pdf
 !bug1250079.pdf
 !bug1473809.pdf
+!issue12120_reduced.pdf
 !pdfjsbad1586.pdf
 !freeculture.pdf
 !issue6006.pdf

test/test_manifest.json

@@ -1991,6 +1991,12 @@
        "type": "eq",
        "about": "MediaBox and CropBox with indirect objects."
     },
+    {  "id": "bug1057544",
+       "file": "pdfs/bug1057544.pdf",
+       "md5": "49ad71b82ead1ee0fe4ddb41aa9e30b4",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue2642",
       "file": "pdfs/issue2642.pdf",
       "md5": "b6679861fdce3bbab0c1fa51bb7f5077",
@@ -4204,6 +4210,12 @@
        "lastPage": 2,
        "type": "eq"
     },
+    {  "id": "issue12120_reduced",
+       "file": "pdfs/issue12120_reduced.pdf",
+       "md5": "b4570dcee26ac3121ad3322e19ed1a6a",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue4883",
       "file": "pdfs/issue4883.pdf",
       "md5": "2fac0d9a189ca5fcef8626153d050be8",