Tweak how fonts with an /Encoding are handled in adjustToUnicode (issue 14048, PR 13277 follow-up)

Currently we only exclude /Encoding entries that also contains a /Differences array, which is the cause of the text-selection problem in the referenced issue.
In order to address this we'll now also exclude /Encoding entries that contain one of the predefined *named* encodings, and no longer require that it also contains a /Differences array.

*Please note:* This patch cases a small "regression" in the `bug1130815-text` test-case, however this is actually an improvement when compared with Adobe Reader and PDFium (in Google Chrome).

test/pdfs/.gitignore

@@ -431,6 +431,7 @@
 !annotation-square-circle.pdf
 !annotation-square-circle-without-appearance.pdf
 !annotation-stamp.pdf
+!issue14048.pdf
 !annotation-fileattachment.pdf
 !annotation-text-widget.pdf
 !annotation-choice-widget.pdf

test/test_manifest.json

@@ -4301,6 +4301,12 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "issue14048",
+       "file": "pdfs/issue14048.pdf",
+       "md5": "770026875a93dc44a187905f4dcd3de2",
+       "rounds": 1,
+       "type": "text"
+    },
     {  "id": "blendmode",
       "file": "pdfs/blendmode.pdf",
       "md5": "5a86e7e9333e93c58abc3f382e1e6ea2",