BCP47 lang tag to OT langtag mapping: zh-MO and zh-Hant-HK are mapped to ZHT

[jungshik]

Test page: http://jungshik.github.io/noto/locltest/locl-test.html

The last three segments in red should all have 'HK' and identical. They're lang-tagged with 'zh-HK', 'zh-Hant-HK' and 'zh-MO'. However, the latter two are mapped to 'ZHT' instead of 'ZHH' ('TW' is shown in place of 'HK' in both Chrome and Firefox).

The heuristics in hb-ot-tag.cc needs a bit of adjustment.

The test font comes from https://github.com/adobe-fonts/locl-test and locl-test.htmll is slightly modified to include zh-Hant-HK and zh-MO.

/cc @kenlunde

[behdad]

cc @brawer

[jungshik]

@kenlunde, do you agree that it's better to map zh-MO (and zh-Hant-Mo) to ZHH instead of ZHT?

[behdad]

Fixed 'zh-Hant-HK'; waiting for confirmation from Ken re MO.

[kenlunde]

@jungshik: Yes, the most appropriate mapping for zh-MO (and friends) would be to ZHH rather than ZHT.

[behdad]

Thanks. All fixed.

[kenlunde]

🍻