Add unicode mapping in the font cmap to have correct chars when printing in pdf (bug 1778484)

It aims to fix https://bugzilla.mozilla.org/show_bug.cgi?id=1778484.

Author: calixteman

src/core/fonts.js

@@ -433,9 +433,11 @@ function convertCidString(charCode, cid, shouldThrow = false) {
  * font that we build
  * 'charCodeToGlyphId' - maps the new font char codes to glyph ids
  */
-function adjustMapping(charCodeToGlyphId, hasGlyph, newGlyphZeroId) {
+function adjustMapping(charCodeToGlyphId, hasGlyph, newGlyphZeroId, toUnicode) {
   const newMap = Object.create(null);
+  const completeMap = Object.create(null);
   const toFontChar = [];
+  const usedGlyphIds = new Set();
   let privateUseAreaIndex = 0;
   let nextAvailableFontCharCode = PRIVATE_USE_AREAS[privateUseAreaIndex][0];
   let privateUseOffetEnd = PRIVATE_USE_AREAS[privateUseAreaIndex][1];
@@ -461,12 +463,28 @@ function adjustMapping(charCodeToGlyphId, hasGlyph, newGlyphZeroId) {
       glyphId = newGlyphZeroId;
     }
 
-    newMap[fontCharCode] = glyphId;
+    // Fix for bug 1778484:
+    // The charcodes are moved into the private area in to fix some rendering
+    // issues (https://github.com/mozilla/pdf.js/pull/9340) but when printing
+    // into pdf the generated will contains wrong chars. We can avoid that in
+    // adding the unicode to the cmap and the print backend will then map the
+    // glyph ids to the correct unicode.
+    let unicode = toUnicode.get(originalCharCode);
+    if (typeof unicode === "string") {
+      unicode = unicode.codePointAt(0);
+    }
+    if (unicode && !usedGlyphIds.has(glyphId)) {
+      completeMap[unicode] = glyphId;
+      usedGlyphIds.add(glyphId);
+    }
+
+    newMap[fontCharCode] = completeMap[fontCharCode] = glyphId;
     toFontChar[originalCharCode] = fontCharCode;
   }
   return {
     toFontChar,
     charCodeToGlyphId: newMap,
+    completeCharCodeToGlyphId: completeMap,
     nextAvailableFontCharCode,
   };
 }
@@ -2914,12 +2932,16 @@ class Font {
       const newMapping = adjustMapping(
         charCodeToGlyphId,
         hasGlyph,
-        glyphZeroId
+        glyphZeroId,
+        this.toUnicode
       );
       this.toFontChar = newMapping.toFontChar;
       tables.cmap = {
         tag: "cmap",
-        data: createCmapTable(newMapping.charCodeToGlyphId, numGlyphsOut),
+        data: createCmapTable(
+          newMapping.completeCharCodeToGlyphId,
+          numGlyphsOut
+        ),
       };
 
       if (!tables["OS/2"] || !validateOS2Table(tables["OS/2"], font)) {
@@ -2992,17 +3014,20 @@ class Font {
     const mapping = font.getGlyphMapping(properties);
     let newMapping = null;
     let newCharCodeToGlyphId = mapping;
+    let newCompleteCharCodeToGlyphId = mapping;
 
     // When `cssFontInfo` is set, the font is used to render text in the HTML
     // view (e.g. with Xfa) so nothing must be moved in the private use area.
     if (!properties.cssFontInfo) {
       newMapping = adjustMapping(
         mapping,
         font.hasGlyphId.bind(font),
-        glyphZeroId
+        glyphZeroId,
+        this.toUnicode
       );
       this.toFontChar = newMapping.toFontChar;
       newCharCodeToGlyphId = newMapping.charCodeToGlyphId;
+      newCompleteCharCodeToGlyphId = newMapping.completeCharCodeToGlyphId;
     }
     const numGlyphs = font.numGlyphs;
 
@@ -3087,7 +3112,10 @@ class Font {
     // OS/2 and Windows Specific metrics
     builder.addTable("OS/2", createOS2Table(properties, newCharCodeToGlyphId));
     // Character to glyphs mapping
-    builder.addTable("cmap", createCmapTable(newCharCodeToGlyphId, numGlyphs));
+    builder.addTable(
+      "cmap",
+      createCmapTable(newCompleteCharCodeToGlyphId, numGlyphs)
+    );
     // Font header
     builder.addTable(
       "head",