Parse cmap table format 14 and handle Unicode Variation Sequences (UVSes)

[Connum]

Description

This PR implements parsing of cmap table format 14 and applying Unicode Variation Sequences (UVSes) during rendering.
Writing is not yet implemented and will be added later in a separate PR.

Motivation and Context

This will get rid of the .null glyph being displayed for variation selectors in text and swap the base character to the desired variation if supported by the font. We'll pass tests CMAP-1 and CMAP-2 of the Unicode test report tool as a result.

How Has This Been Tested?

Added tests, tested with fonts, ran the Unicode test report (with #568 implemented in a test branch).

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I did npm run test and all tests passed green (including code styling checks).
• I have added tests to cover my changes.
• My change requires a change to the documentation.
• I have updated the README accordingly.
• I have read the CONTRIBUTING document.

[ILOVEPIE]

I'll review it after work today

[ILOVEPIE]

I've written a few comments/questions, once those are discussed I will do an approving review. They aren't necessarily show-stoppers so I'm not going to request changes, but we should discuss them.

[Connum]

rebased on current master

[ILOVEPIE]

Looks good to me.