Rename FontFace to FontFaceObject

This name clashes with the FontFace constructor from the Font Loading CSS module:
http://dev.w3.org/csswg/css-font-loading/#font-face-constructor
Use Font Loading API if available

http://dev.w3.org/csswg/css-font-loading/
Fixes enabling pdfBug
Merge pull request #5367 from yurydelendik/fixpdfbug

Fixes enabling pdfBug
Fixes examples comments.
Merge pull request #5366 from Rob--W/use-font-loader-api

Use font loader api