[editor] Add an Ink editor

- Approximate the drawn curve by a set of Bezier curves in using
  js code from https://github.com/soswow/fit-curves.
  The code has been slightly modified in order to make the linter
  happy.

src/shared/util.js

@@ -57,6 +57,7 @@ const AnnotationEditorPrefix = "pdfjs_internal_editor_";
 const AnnotationEditorType = {
   NONE: 0,
   FREETEXT: 3,
+  INK: 15,
 };
 
 // Permission flags from Table 22, Section 7.6.3.2 of the PDF specification.