Add keyboard support for Khiamniungan Naga (kix)

[ToluAyodele]

Downstream task: https://phabricator.wikimedia.org/T428856

[srish]

Thanks @ToluAyodele for the PR! I have a few questions before I can approve this:

• Right now we can type ǜ but not Ǜ. I am wondering if we need the capital versions too here.
• Could you check the orthography source and confirm what the full list should be? And if we really only need three characters. It might be worth looking into https://en.wikipedia.org/wiki/Patsho_Khiamniungan#Writing_system and https://en.wikivoyage.org/wiki/Khiamniungan_Naga_phrasebook#Written_language. I can also double check with the contributor.
• Could you confirm if the indentation format of the code lines you have added/modified match the existing files?

[srish]

Rule wise changes are looking good now. Requesting a documentation and few more indentation and formatting related changes. See comments inline.

[srish]

Documentation link needs to be added.

[srish]

it looks like the comments are column aligned. Rest of the repo doesn't follow this convention.

[srish]

Fixture style here diverges from the rest of the file. We can add input, output and description in single lines and then remove all the comments from this file. You could try adding two more test cases - capital tone-marked vowels (A~\E~-I~^O~/U~\ → ÀĒÎÓÙ) and a real word (h~u~-he~^i → hǖhêi).

[srish]

Should be 2 given this is the length of largest regex sequence in the patterns.