[Editor] Improve curve smoothing for Ink tool (bug 1789443)

- Remove the dependency on fit-curve;
- Improve the way to draw the current line in using a Path2D and
  in clearing only the last part of the curve instead of clearing
  all the canvas;
- Smooth the curve when drawing to avoid to have some changes after
  the drawing ends;
- Make the smoothing a bit less agressive.

web/viewer-geckoview.html

@@ -48,7 +48,6 @@ See https://github.com/adobe-type-tools/cmap-resources
           "pdfjs/": "../src/",
           "pdfjs-lib": "../src/pdf.js",
           "pdfjs-web/": "./",
-          "pdfjs-fitCurve": "../build/dev-fitCurve/fit_curve.js",
 
           "web-annotation_editor_params": "./stubs-geckoview.js",
           "web-com": "./genericcom.js",

web/viewer.html

@@ -59,7 +59,6 @@ See https://github.com/adobe-type-tools/cmap-resources
           "pdfjs/": "../src/",
           "pdfjs-lib": "../src/pdf.js",
           "pdfjs-web/": "./",
-          "pdfjs-fitCurve": "../build/dev-fitCurve/fit_curve.js",
 
           "web-annotation_editor_params": "./annotation_editor_params.js",
           "web-com": "./genericcom.js",