Khmer and Burmese languages not rendered correctly

[Argh4k]

mapbox-gl-js version: 0.53.1

browser: Firefox (Ubuntu 16.04)

Steps to Trigger Behavior

1. Download zip containing examples together with pbf encoded fonts
   fontTest.zip
2. Host locally folder with fonts from zip on port 8080
3. Open provided html pages

Expected Behavior

Label for Phnom Penh (Cambodia capital) is rendered correctly using proper fonts.

Label for Naypyidaw (Myanmar capital) is rendered correctly using proper fonts.

Actual Behavior

Label for Phnom Penh is rendered incorrectly using google Noto Sans Khmer font (https://www.google.com/get/noto/#sans-khmr) on the right, and Khmer font (https://fonts.google.com/specimen/Khmer) on the left.

Label for Naypyidaw is rendered incorrectly using google Noto Sans Myanmar font (https://www.google.com/get/noto/#sans-mymr) on the left and Padauk font (https://fonts.google.com/?subset=myanmar) on the right.

[mapcarta]

We're also experiencing problems with both Khmer and Burmese, but in our case text is not appearing at all on all browsers. We're using the latest version of Mapbox GL JS, 1.3.2.

For examples, see the Mapcarta pages for the Siam Reap and Mandalay Airports which have missing labels:

• Siam Reap Airport (អាកាសយានដ្ឋាន​អន្តរជាតិ​សៀមរាប)
• Mandalay Chanmyathazi Airport (မန္တလေးချမ်းမြသာစည်လေဆိပ်)

[kkaefer]

See #4009 and mapbox/mapbox-gl-native#7774 for more background.