[lianghai]

Resolves: #234.

See also: https://harfbuzz.github.io/harfbuzz-hb-ot-layout.html.

Notes:

• Had to hard-code HB_OT_MAX_TAGS_PER_LANGUAGE and HB_OT_MAX_TAGS_PER_SCRIPT, because I couldn’t figure out how to expose them through Emscripten. Left links for now to point to the HB documentation.
• Haven’t handled the nullability of hb_ot_tags_from_script_and_language()’s language parameter. The optionality of other (in)out parameters doesn’t seem that relevant to the JS binding.
• It seems language_from_string() can be used here for hb_ot_tags_from_script_and_language()’s language parameter? But a parallel function for script doesn’t exist, so I followed Buffer.setLanguage() and .setScript()’s parallel logic instead.
• Haven’t figured out when hb_ot_tags_from_script_and_language() actually produces multiple language tags. Added a few typical cases for testing.
• The first argument to it() can be the tested function itself, so the function’s name is used, which may be more maintainable when there isn’t much to say about a test. Also an arrow function as the second argument may be less cluttering?

[khaledhosny]

Thanks!