Use harfbuzzjs instead of fontkit

[papandreou]

We use fontkit for getting the codepoints in a font and information about the variation axes. We can use harfbuzzjs for that instead and remove a heavy dependency.

Prerequisite: harfbuzz/harfbuzzjs#77

[github-actions]

Pull Request Test Coverage Report for Build 4708973237

• 22 of 22 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 90.066%

---

Totals
Change from base Build 4644324050:	0.1%
Covered Lines:	1154
Relevant Lines:	1221

---

💛 - Coveralls