[Annotation] Fix printing/saving for annotations containing some non-ascii chars and with no fonts to handle them (bug 1666824)

- For text fields
 * when printing, we generate a fake font which contains some widths computed thanks to
   an OffscreenCanvas and its method measureText.
   In order to avoid to have to layout the glyphs ourselves, we just render all of them
   in one call in the showText method in using the system sans-serif/monospace fonts.
 * when saving, we continue to create the appearance streams if the fonts contain the char
   but when a char is missing, we just set, in the AcroForm dict, the flag /NeedAppearances
   to true and remove the appearance stream. This way, we let the different readers handle
   the rendering of the strings.
- For FreeText annotations
  * when printing, we use the same trick as for text fields.
  * there is no need to save an appearance since Acrobat is able to infer one from the
    Content entry.

src/core/xref.js

@@ -42,18 +42,34 @@ class XRef {
     this._cacheMap = new Map(); // Prepare the XRef cache.
     this._pendingRefs = new RefSet();
     this.stats = new DocStats(pdfManager.msgHandler);
-    this._newRefNum = null;
+    this._newPersistentRefNum = null;
+    this._newTemporaryRefNum = null;
   }
 
-  getNewRef() {
-    if (this._newRefNum === null) {
-      this._newRefNum = this.entries.length || 1;
+  getNewPersistentRef(obj) {
+    // When printing we don't care that much about the ref number by itself, it
+    // can increase for ever and it allows to keep some re-usable refs.
+    if (this._newPersistentRefNum === null) {
+      this._newPersistentRefNum = this.entries.length || 1;
     }
-    return Ref.get(this._newRefNum++, 0);
+    const num = this._newPersistentRefNum++;
+    this._cacheMap.set(num, obj);
+    return Ref.get(num, 0);
   }
 
-  resetNewRef() {
-    this._newRefNum = null;
+  getNewTemporaryRef() {
+    // When saving we want to have some minimal numbers.
+    // Those refs are only created in order to be written in the final pdf
+    // stream.
+    if (this._newTemporaryRefNum === null) {
+      this._newTemporaryRefNum = this.entries.length || 1;
+    }
+    return Ref.get(this._newTemporaryRefNum++, 0);
+  }
+
+  resetNewTemporaryRef() {
+    // Called once saving is finished.
+    this._newTemporaryRefNum = null;
   }
 
   setStartXRef(startXRef) {